View source for Software:Exposure Notification

{{short description|Initiative for mobile device-based privacy-preserving contact tracing}}
{{Infobox protocol
|name=Exposure Notification
|caption=
|standard=
|developer={{Unbulleted list|[[Company:Apple Inc.|Apple Inc.]]|[[Company:Google|Google]]}}
|introdate={{Start date|2020|04|10}}
|industry=[[Software:Digital contact tracing|Digital contact tracing]]
|hardware=[[Software:Android (operating system)|Android]] & [[Software:IOS|iOS]] smartphones
|range=~{{convert|10|m|abbr=on}}<ref>{{Cite web|url=https://blog.nordicsemi.com/getconnected/things-you-should-know-about-bluetooth-range|title=Things You Should Know About Bluetooth Range|last=Sponås|first=Jon Gunnar|website=blog.nordicsemi.com|language=en-gb|access-date=2020-04-12}}</ref>
|website=|image=Exposure_Notifications.png}}

The '''(Google/Apple) Exposure Notification''' ('''GAEN''') system,<ref>{{Cite web|title=Exposure Notification API launches to support public health agencies|url=https://blog.google/inside-google/company-announcements/apple-google-exposure-notification-api-launches/|date=2020-05-20|website=Google|language=en|access-date=2020-05-21}}</ref><ref>{{Cite web|title=ExposureNotification {{!}} Apple Developer Documentation|url=https://developer.apple.com/documentation/exposurenotification|website=developer.apple.com|access-date=2020-05-21}}</ref><ref>{{Cite web|title=Exposure Notifications: Helping fight COVID-19 - Google|url=https://www.google.com/intl/en_us/covid19/exposurenotifications/|access-date=2020-07-31|website=Exposure Notifications: Helping fight COVID-19 - Google|language=en}}</ref> originally known as the '''Privacy-Preserving Contact Tracing Project''',<ref>{{cite web |url=https://www.apple.com/covid19/contacttracing/ |title=Privacy-Preserving Contact Tracing |date=10 April 2020 |publisher=Apple }}</ref><ref>{{cite web |title=Contact Tracing – Bluetooth Specification |date=2020-04-10 |edition=Preliminary |url=https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ContactTracing-BluetoothSpecification.pdf |access-date=2020-04-10 |url-status=live |archive-url=https://web.archive.org/web/20200410171559/https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ContactTracing-BluetoothSpecification.pdf |archive-date=2020-04-10}}</ref> is a framework and protocol specification developed by [[Company:Apple Inc.|Apple Inc.]] and [[Company:Google|Google]] to facilitate [[Software:Digital contact tracing|digital contact tracing]] during the COVID-19 pandemic. When used by health authorities, it augments more traditional [[Medicine:Contact tracing|contact tracing]] techniques by automatically logging close approaches among notification system users using [[Software:Android (operating system)|Android]] or [[Software:IOS|iOS]] [[Engineering:Smartphone|smartphone]]s. Exposure Notification is a decentralized reporting protocol built on a combination of [[Bluetooth Low Energy]] technology and privacy-preserving [[Cryptography|cryptography]]. It is an opt-in feature within COVID-19 apps developed and published by authorized health authorities.<ref>{{cite web |url=https://social.techcrunch.com/2020/04/10/apple-and-google-are-launching-a-joint-covid-19-tracing-tool/ |title=Apple and Google are launching a joint COVID-19 tracing tool for iOS and Android |work=TechCrunch |date=10 April 2020 |language=en-US |access-date=2020-04-10 |archive-date=2020-05-22 |archive-url=https://web.archive.org/web/20200522033457/http://techcrunch.com/2020/04/10/apple-and-google-are-launching-a-joint-covid-19-tracing-tool/ |url-status=dead }}</ref><ref name="CNET 4-10-2020">{{cite web |title=Apple and Google are building coronavirus tracking tech into iOS and Android |publisher=CNET |date=2020-04-10 |author-last1=Sherr |author-first1=Ian |author-first2=Richard |author-last2=Nieva |url=https://www.cnet.com/news/apple-and-google-are-building-coronavirus-tracking-tech-into-ios-and-android/ |access-date=2020-04-10 |url-status=live |archive-url=https://web.archive.org/web/20200410202158/https://www.cnet.com/news/apple-and-google-are-building-coronavirus-tracking-tech-into-ios-and-android/ |archive-date=2020-04-10}}</ref> Unveiled on April 10, 2020, it was made available on iOS on May 20, 2020 as part of the [[Software:IOS 13|iOS 13]].5 update<ref name=":1">{{Cite news|title=COVID-19 exposure notification settings begin to go live for iOS users with new update|url=https://social.techcrunch.com/2020/05/20/covid-19-exposure-notification-settings-begin-to-go-live-for-ios-users-with-new-update/|website=TechCrunch|language=en-US|access-date=2020-05-21}}</ref> and on December 14, 2020 as part of the [[Software:IOS 12|iOS 12]].5 update for older iPhones.<ref>{{Cite web|last=Miller|first=Chance|date=2020-12-14|title=Apple releases iOS 12.5 for older iPhones with support for COVID-19 exposure notifications|url=https://9to5mac.com/2020/12/14/apple-releases-ios-12-5-for-older-iphones-with-support-for-covid-19-exposure-notifications/|access-date=2021-01-05|website=9to5Mac|language=en-US}}</ref> On Android, it was added to devices via a [[Software:Google Play Services|Google Play Services]] update, supporting all versions since [[Software:Android Marshmallow|Android Marshmallow]].

The Apple/Google protocol is similar to the [[Decentralized Privacy-Preserving Proximity Tracing]] (DP-3T) protocol created by the European DP-3T consortium and the [[Software:TCN Protocol|Temporary Contact Number]] (TCN) protocol by Covid Watch, but is implemented at the [[Operating system|operating system]] level, which allows for more efficient operation as a background [[Process (computing)|process]].<ref name=":3">{{Cite web|url=https://social.techcrunch.com/2020/04/24/apple-and-google-update-joint-coronavirus-tracing-tech-to-improve-user-privacy-and-developer-flexibility/|title=Apple and Google update joint coronavirus tracing tech to improve user privacy and developer flexibility|website=TechCrunch|date=24 April 2020|language=en-US|access-date=2020-04-26|archive-date=2021-06-04|archive-url=https://web.archive.org/web/20210604040434/https://techcrunch.com/2020/04/24/apple-and-google-update-joint-coronavirus-tracing-tech-to-improve-user-privacy-and-developer-flexibility/|url-status=dead}}</ref><ref name=":4">{{Cite web|url=https://www.cnbc.com/2020/04/28/apple-iphone-contact-tracing-how-it-came-together.html|title=How a handful of Apple and Google employees came together to help health officials trace coronavirus|last=Farr|first=Christina|date=2020-04-28|website=CNBC|language=en|access-date=2020-04-29}}</ref><ref>{{Cite web|date=2020-04-06|title=Private Contact Tracing Protocols Compared: DP-3T and CEN|url=https://www.zfnd.org/blog/private-contact-tracing-protocols-compared/|website=Zcash Foundation|language=en}}</ref> Since May 2020, a variant of the DP-3T protocol is supported by the Exposure Notification Interface.<ref>{{cite web|url=https://www.esat.kuleuven.be/cosic/sites/corona-app/wp-content/uploads/sites/8/2020/08/coronalert_belgium_description_v1_2.pdf|title=Coronalert: A Distributed Privacy-Friendly Contact Tracing App for Belgium : Corona App Task Force Version 1.2|date=5 August 2020|website=Esat.kuleuven.be|access-date=27 June 2022}}</ref> Other protocols are constrained in operation because they are not privileged over normal [[Mobile app|apps]]. This leads to issues, particularly on iOS devices where digital contact tracing apps running in the background experience significantly degraded performance.<ref>{{Cite web|title=Want the COVID-19 tracing app to work properly? Keep your iPhone charged|url=https://www.abc.net.au/news/2020-04-26/coronavirus-tracing-app-covidsafe-apple-iphone-covid-19/12187448|last=Bogle|first=technology reporter Ariel|date=2020-04-26|website=ABC News|language=en-AU|access-date=2020-04-26}}</ref><ref name=":5">{{Cite web|title=BlueTrace: A privacy-preserving protocol for community-driven contact tracing across borders|url=https://bluetrace.io/static/bluetrace_whitepaper-938063656596c104632def383eb33b3c.pdf|last=Jason Bay, Joel Kek, Alvin Tan, Chai Sheng Hau, Lai Yongquan, Janice Tan, Tang Anh Quy|website=Government Technology Agency|access-date=12 April 2020}}</ref><ref name=":8">{{Cite web|title=How COVIDsafe app tracks people 1.5m from you|url=https://www.thechronicle.com.au/news/first-look-at-coronavirus-tracing-app/4002858/|website=Chronicle|language=en|access-date=2020-04-26}}</ref> The joint approach is also designed to maintain interoperability between Android and iOS devices, which constitute nearly all of the market.

The ACLU stated the approach "appears to mitigate the worst privacy and centralization risks, but there is still room for improvement".<ref>{{cite news |title=ACLU Comment On Apple/Google COVID-19 Contact Tracing Effort |url=https://www.aclu.org/press-releases/aclu-comment-applegoogle-covid-19-contact-tracing-effort |access-date=2020-04-22 |work=ACLU |date=2020 |language=en}}</ref> In late April, Google and Apple shifted the emphasis of the naming of the system, describing it as an "exposure notification service", rather than "contact tracing" system.<ref>{{Cite web|url=https://www.vox.com/recode/2020/4/24/21234420/apple-google-contact-tracing-exposure-notification-update|title=Apple and Google's new contact tracing tool is almost ready. Just don't call it a contact tracing tool.|last=Morrison|first=Sara|date=2020-04-24|website=Vox|language=en|access-date=2020-04-27}}</ref>

== Technical specification ==
Digital contact tracing protocols typically have two major responsibilities: encounter logging and infection reporting.<ref name=":5" /> Exposure Notification only involves encounter logging which is a decentralized architecture. The majority of infection reporting is centralized in individual app implementations.<ref>{{Cite web|title=Android Contact Tracing API|url=https://blog.google/documents/55/Android_Contact_Tracing_API.pdf|date=2020-04-10|website=Blog.google|access-date=2020-05-08}}</ref>

To handle encounter logging, the system uses Bluetooth Low Energy to send tracking messages to nearby devices running the protocol to discover encounters with other people. The tracking messages contain unique identifiers that are encrypted with a secret daily key held by the sending device. These identifiers change every 15–20 minutes as well as Bluetooth [[MAC address]] in order to prevent tracking of clients by malicious third parties through observing static identifiers over time.{{Cn|date=March 2023}}

The sender's daily encryption keys are generated using a random number generator.<ref name=":0">{{Cite web|url=https://social.techcrunch.com/2020/04/24/apple-and-google-update-joint-coronavirus-tracing-tech-to-improve-user-privacy-and-developer-flexibility/|title=Apple and Google update joint coronavirus tracing tech to improve user privacy and developer flexibility|website=TechCrunch|date=24 April 2020|language=en-US|access-date=2020-04-27|archive-date=2021-06-04|archive-url=https://web.archive.org/web/20210604040434/https://techcrunch.com/2020/04/24/apple-and-google-update-joint-coronavirus-tracing-tech-to-improve-user-privacy-and-developer-flexibility/|url-status=dead}}</ref> Devices record received messages, retaining them locally for 14 days. If a user tests positive for infection, the last 14 days of their daily encryption keys can be uploaded to a central server, where it is then broadcast to all devices on the network. The method through which daily encryption keys are transmitted to the central server and broadcast is defined by individual app developers. The Google-developed reference implementation calls for a health official to request a [[One-time password|one-time]] verification code (VC) from a ''verification server'', which the user enters into the encounter logging app. This causes the app to obtain a cryptographically signed certificate, which is used to authorize the submission of keys to the central reporting server.<ref>{{Cite web|title=Exposure Notifications verification server|url=https://developers.google.com/android/exposure-notifications/verification-system|access-date=2020-09-01|website=Google Developers|language=en}}</ref>

The received keys are then provided to the protocol, where each client individually searches for matches in their local encounter history. If a match meeting certain risk parameters is found, the app notifies the user of potential exposure to the infection.<ref>{{Cite web|title=Exposure Notification Frequently Asked Questions Preliminary — Subject to Modification and Extension|url=https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FAQv1.1.pdf|date=2020-05-01|website=Apple|access-date=2020-05-08|archive-date=2020-05-06|archive-url=https://web.archive.org/web/20200506015327/https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FAQv1.1.pdf|url-status=dead}}</ref> Google and Apple intend to use the received signal strength (RSSI) of the beacon messages as a source to infer proximity.<ref>{{Cite magazine|url=https://www.wired.com/story/apple-google-contact-tracing-strengths-weaknesses/|title=Is Apple and Google's Covid-19 Contact Tracing a Privacy Risk?|magazine=Wired|access-date=2020-04-18|language=en|issn=1059-1028}}</ref> RSSI and other signal metadata will also be encrypted to resist deanonymization attacks.<ref name=":0" />

=== Version 1.0 ===
To generate encounter identifiers, first a persistent 32-byte private ''Tracing Key'' (<math>tk</math>) is generated by a client. From this a 16 byte ''Daily Tracing Key'' is derived using the algorithm ''<math>dtk_i = HKDF(tk, NULL, \text{'CT-DTK'}||D_i, 16)</math>'', where <math>HKDF(\text{Key, Salt, Data, OutputLength})</math> is a [[HKDF]] function using SHA-256, and <math>D_i</math> is the ''day number'' for the 24-hour window the broadcast is in starting from Unix Epoch Time. These generated keys are later sent to the central reporting server should a user become infected.<ref name=":9">{{Cite web|date=April 2020|title=Contact Tracing - Cryptography Specification|url=https://blog.google/documents/56/Contact_Tracing_-_Cryptography_Specification.pdf|access-date=2020-06-14}}</ref>

From the daily tracing key a 16-byte temporary ''Rolling Proximity Identifier'' is generated every 10 minutes with the algorithm <math>RPI_{i,j} = \text{Truncate}(HMAC(dtk_i, \text{'CT-RPI'}||TIN_j),16)</math>, where <math>HMAC(\text{Key, Data})</math> is a [[HMAC]] function using SHA-256, and <math>TIN_j</math> is the ''time interval number'', representing a unique index for every 10 minute period in a 24-hour day. The Truncate function returns the first 16 bytes of the HMAC value. When two clients come within proximity of each other they exchange and locally store the current <math>RPI_{i,j}</math> as the encounter identifier.<ref name=":9" />

Once a registered health authority has confirmed the infection of a user, the user's Daily Tracing Key for the past 14 days is uploaded to the central reporting server. Clients then download this report and individually recalculate every Rolling Proximity Identifier used in the report period, matching it against the user's local encounter log. If a matching entry is found, then contact has been established and the app presents a notification to the user warning them of potential infection.<ref name=":9" />

=== Version 1.1 ===
Unlike version 1.0 of the protocol, version 1.1 does not use a persistent ''tracing key'', rather every day a new random 16-byte ''Temporary Exposure Key'' <u>(</u><math>tek_i</math>) is generated.  This is analogous to the ''daily tracing key'' from version 1.0. Here <math>i</math> denotes the  time is discretized in 10 minute intervals starting from Unix Epoch Time. From this two 128-bit keys are calculated, the ''Rolling Proximity Identifier Key'' (<math>RPIK_i</math>) and the ''Associated Encrypted Metadata Key'' (<math>AEMK_i</math>).   <math>RPIK_i</math> is calculated with the algorithm  <math>RPIK_i = HKDF(tek_i, NULL, \text{'EN-RPIK'},16)</math>, and  <math>AEMK_i</math> using the algorithm<math>AEMK_i = HKDF(tek_i, NULL, \text{'EN-AEMK'},16)</math>.<ref name=":7" />

From these values a temporary ''Rolling Proximity Identifier'' (<math>RPI_{i,j}</math>) is generated every time the BLE [[MAC address]] changes, roughly every 15–20 minutes. The following algorithm is used: <math>RPI_{i,j} = AES128(RPIK_i, \text{'EN-RPI'} || \mathtt{0x000000000000} || ENIN_j)</math>, where <math>AES128(\text{Key, Data})</math> is an [[Advanced Encryption Standard|AES]] cryptography function with a 128-bit key, the data is one 16-byte block,  <math>j</math> denotes the Unix Epoch Time at the moment the roll occurs, and  <math>ENIN_j</math> is the corresponding 10-minute interval number. Next, additional ''Associated Encrypted Metadata'' is encrypted. What the metadata represents is not specified, likely to allow the later expansion of the protocol. The following algorithm is used: <math>\text{Associated Encrypted Metadata}_{i,j} = AES128\_CTR(AEMK_i, RPI_{i,j}, \text{Metadata})</math>, where <math>AES128\_CTR(\text{Key, IV, Data})</math> denotes AES encryption with a 128-bit key in CTR mode. The Rolling Proximity Identifier and the Associated Encrypted Metadata are then combined and broadcast using BLE. Clients exchange and log these payloads.<ref name=":7" />

Once a registered health authority has confirmed the infection of a user, the user's Temporary Exposure Keys <math>tek_i</math> and their respective interval numbers <math>i</math> for the past 14 days are uploaded to the central reporting server. Clients then download this report and individually recalculate every Rolling Proximity Identifier starting from interval number  <math>i</math>, matching it against the user's local encounter log. If a matching entry is found, then contact has been established and the app presents a notification to the user warning them of potential infection.<ref name=":7" />

=== Version 1.2 ===
Version 1.2 of the protocol is identical to version 1.1, only introducing minor terminology changes.<ref name=":7">{{Cite web|title=Exposure Notification - Cryptography Specification|url=https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-CryptographySpecificationv1.2.pdf|date=April 2020|website=Apple|access-date=2020-05-22}}</ref>

== Privacy ==
Preservation of privacy was referred to as a major component of the protocol; it is [[Data anonymization|designed]] so that no personally identifiable information can be obtained about the user or their device.<ref>{{Cite web|title=Apple and Google update joint coronavirus tracing tech to improve user privacy and developer flexibility|url=https://social.techcrunch.com/2020/04/24/apple-and-google-update-joint-coronavirus-tracing-tech-to-improve-user-privacy-and-developer-flexibility/|website=TechCrunch|date=24 April 2020|language=en-US|access-date=2020-05-21|archive-date=2021-06-04|archive-url=https://web.archive.org/web/20210604040434/https://techcrunch.com/2020/04/24/apple-and-google-update-joint-coronavirus-tracing-tech-to-improve-user-privacy-and-developer-flexibility/|url-status=dead}}</ref><ref name="CNET 4-10-2020" /><ref name=":6">{{Cite web|title=Why countries keep bowing to Apple and Google's contact tracing app requirements|url=https://www.theverge.com/interface/2020/5/8/21250744/apple-google-contact-tracing-england-germany-exposure-notification-india-privacy|last=Newton|first=Casey|date=2020-05-08|website=The Verge|language=en|access-date=2020-05-21}}</ref><ref>{{Cite web|title=Apple, Google announce new privacy features for coronavirus tracking tech|url=https://www.cnet.com/news/apple-google-announce-new-privacy-features-for-coronavirus-tracking-tech/|last=Sherr|first=Ian|website=CNET|language=en|access-date=2020-05-21}}</ref> Apps implementing Exposure Notification are only allowed to collect personal information from users on a voluntary basis.<ref name=":2" /> Consent must be obtained by the user to enable the system or publicize a positive result through the system, and apps using the system are prohibited from collecting location data.<ref name=":14">{{Cite news|title=Apple and Google release sample code, UI and detailed policies for COVID-19 exposure-notification apps|url=https://social.techcrunch.com/2020/05/04/apple-and-google-release-sample-code-and-detailed-policies-for-covid-19-exposure-notification-apps/|access-date=2020-09-01|website=TechCrunch|language=en-US}}</ref> As an additional measure, the companies stated that it would [[Social:Sunset provision|sunset]] the protocol by-region once they determine that it is "no longer needed".<ref name="newton-2020-04-14">{{Cite web|last=Newton|first=Casey|date=2020-04-14|title=Apple and Google have a clever way of encouraging people to install contact-tracing apps for COVID-19|url=https://www.theverge.com/interface/2020/4/14/21219289/apple-google-contact-tracing-app-android-ios-pros-cons-quarantine-testing|access-date=2020-04-15|website=The Verge|language=en}}</ref>

The [[Organization:Electronic Frontier Foundation|Electronic Frontier Foundation]] showed concerns the protocol was vulnerable to "linkage attacks", where sufficiently capable third parties who had recorded beacon traffic may retroactively be able to turn this information into tracking information, for only areas in which they had already recorded beacons, for a limited time segment and for only users who have disclosed their COVID-19 status, once a device's set of daily encryption keys have been revealed.<ref>{{Cite web|title=Apple and Google's COVID-19 Exposure Notification API: Questions and Answers|url=https://www.eff.org/deeplinks/2020/04/apple-and-googles-covid-19-exposure-notification-api-questions-and-answers|last=Gebhart|first=Bennett Cyphers and Gennie|date=2020-04-28|website=Electronic Frontier Foundation|language=en|access-date=2020-05-21}}</ref>

On April 16, the [[Social:European Union|European Union]] started the process of assessing the proposed system for compatibility with privacy and data protection laws, including the [[General Data Protection Regulation]] (GDPR).<ref>{{Cite news|last=Drozdiak|first=Natalia|date=16 April 2020|title=Google, Apple Covid-19 Tracking Tech Faces EU Scrutiny|url=https://www.bloomberg.com/news/articles/2020-04-16/google-apple-covid-19-tracking-tech-faces-eu-scrutiny|newspaper=Bloomberg.com}}</ref> On April 17, 2020, the UK's Information Commissioner's Office, a supervisory authority for data protection, published an opinion analyzing both Exposure Notification and the [[Decentralized Privacy-Preserving Proximity Tracing]] protocol, stating that the systems are "aligned with the principles of data protection by design and by default" (as mandated by the GDPR).<ref>{{Cite web|last=ICO|date=17 April 2020|title=Apple and Google joint initiative on COVID-19 contact tracing technology|url=https://ico.org.uk/media/about-the-ico/documents/2617653/apple-google-api-opinion-final-april-2020.pdf|website=Information Commissioner's Office}}</ref>

== Deployment ==
Exposure Notification is compatible with Android devices supporting [[Bluetooth Low Energy]] and running Android 6.0 "Marshmallow" and newer with [[Software:Google Mobile Services|Google Mobile Services]]. It is serviced via updates to [[Software:Google Play Services|Google Play Services]], ensuring compatibility with the majority of Android devices released outside of Mainland China, and not requiring it to be integrated into Android firmware updates (which would hinder deployment by relying on individual OEMs). It is not compatible with devices that do not have GMS, such as [[Company:Huawei|Huawei]] devices released since May 2019.<ref>{{Cite web |last=Bohn |first=Dieter |date=2020-04-13 |title=Android phones will get the COVID-19 tracking updates via Google Play |url=https://www.theverge.com/2020/4/13/21220033/android-covid-19-tracking-updates-google-play-contact-tracing |access-date=2020-04-16 |website=The Verge |language=en}}</ref><ref>{{Cite web |date=2020-05-25 |title=Apple And Google's Contact Tracing Software Won't Work On Some Huawei Devices |url=https://www.gizmodo.com.au/2020/05/apple-google-coronavirus-huawei-exposure-notification-system/ |access-date=2020-10-07 |website=Gizmodo Australia |language=en-AU}}</ref>  On iOS, EN is serviced via operating system updates.<ref name=":1" /> It was first introduced as part of [[Software:IOS 13|iOS 13]].5 on May 20, 2020.<ref>{{Cite web|last=Gartenberg|first=Chaim|date=2020-04-14|title=Here's how Apple and Google will track the coronavirus with Bluetooth|url=https://www.theverge.com/2020/4/14/21220644/apple-googles-bluetooth-low-energy-le-coronavirus-tracking-contact-tracing|access-date=2020-09-01|website=The Verge|language=en}}</ref><ref name=":24">{{Cite web |last=Miller |first=Chance |date=2020-12-14 |title=Apple releases iOS 12.5 for older iPhones with support for COVID-19 exposure notifications |url=https://9to5mac.com/2020/12/14/apple-releases-ios-12-5-for-older-iphones-with-support-for-covid-19-exposure-notifications/ |access-date=2020-12-14 |website=9to5Mac |language=en-US}}</ref> In December 2020, Apple released iOS 12.5, which [[Backporting|backported]] EN support to iPhone models that cannot be upgraded to iOS 13, including [[Engineering:IPhone 6|iPhone 6]] and older.<ref name=":24" />

Exposure Notification apps may only be released by public health authorities. To discourage fragmentation, each country will typically be restricted to one app, although Apple and Google stated that they would accommodate regionalized approaches if a country elects to do so.<ref name=":14" /> Apple and Google released reference implementations for apps utilizing the system, which can be used as a base.<ref name=":14" />

On September 1, 2020, the consortium announced "Exposure Notifications Express" (EN Express), a system designed to ease adoption of the protocol by health authorities by removing the need to develop an app themselves. Under this system, a health authority provides parameters specific to their implementation (such as thresholds, branding, messaging, and key servers), which is then processed to generate the required functionality. On Android, this data is used to generate an app, and a configuration profile that can also be deployed to users via Google Play Services without a dedicated app.<ref name=":25" /> On iOS, the functionality is integrated directly at the system level on iOS 13.7 and newer without a dedicated app.<ref name=":15">{{Cite web|last=Brandom|first=Russell|date=2020-09-01|title=Apple and Google announce new automatic app system to track COVID exposures|url=https://www.theverge.com/2020/9/1/21410281/apple-google-coronavirus-exposure-notification-contact-tracing-app-system|access-date=2020-09-01|website=The Verge|language=en}}</ref> On December 14, 2020, Apple released iOS 12.5, bringing support for Exposure Notifications to older iPhones.{{cn|date=October 2022}}

The last information update on the “Exposure Notification  Systems” partnership was a year end review issued by Google in December 2020:<ref>{{Cite web|url=https://blog.google/inside-google/covid-19/exposure-notifications-end-year-update/|title = Exposure Notifications: End of year update|date = 11 December 2020}}</ref> "we plan to keep you updated here with new information again next year". Nothing has however been issued on the one year anniversary of the launch of the “Exposure Notification Interface” API in spite of important changes on the pandemic front such as vaccination, variants, digital health passports, app adoption challenges as well as growing interest for tracking QR codes (and notifying from that basis) on a mostly airborne transmitted virus.{{Original research inline|date=June 2021}} The Frequently Asked Questions (FAQ) published document has not been revised since May 2020.<ref>{{Cite web |url=https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FAQv1.0.pdf |title=Archived copy |access-date=2020-04-27 |archive-date=2020-04-26 |archive-url=https://web.archive.org/web/20200426210251/https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FAQv1.0.pdf |url-status=dead }}</ref> Basic support remains provided through the apps store released by authorized public health agencies, including enforcement of the personal privacy protection framework as demonstrated on the UK NHS challenge in support of their contact tracers.<ref>{{Cite news|url=https://www.bbc.com/news/technology-56713017|title = NHS Covid-19 app update blocked for breaking Apple and Google's rules|work = BBC News}}</ref>

In June 2021, Google faced allegations that it had automatically downloaded Massachusetts' "MassNotify" app to Android devices without user consent. Google clarified that it had not actually downloaded the app to user devices, and that Google Play Services was being used to deploy an EN Express configuration profile that would allow it to be enabled via the Google Settings app without needing to download a separate app.<ref name=":25">{{Cite web|last=Amadeo|first=Ron|date=2021-06-21|title=Even creepier COVID tracking: Google silently pushed app to users' phones [Updated]|url=https://arstechnica.com/gadgets/2021/06/even-creepier-covid-tracking-google-silently-pushed-app-to-users-phones/|access-date=2021-06-22|website=Ars Technica|language=en-us}}</ref>

== Adoption ==

As of May 21, at least 22 countries had received access to the protocol.<ref name=":2">{{Cite web|title=Google and Apple unite to help countries like Australia fix their contact tracing apps|url=https://www.abc.net.au/news/2020-05-21/google-apple-technology-help-coronavirus-contact-tracing/12271728|date=2020-05-21|website=ABC News|language=en-AU|access-date=2020-05-21}}</ref> Switzerland and Austria were among the first to back the protocol.<ref>{{Cite web|title=Switzerland, Austria align with 'Gapple' on corona contact tracing|url=https://www.reuters.com/article/health-coronavirus-europe-tech/switzerland-austria-align-with-gapple-on-corona-contact-tracing-idUSL3N2CA36L|date=2020-04-22|work=Reuters|language=en|access-date=2020-05-06}}</ref> On April 26, after initially backing PEPP-PT, Germany announced it would back Exposure Notification,<ref name="reuters-2020-04-26">{{Cite news|date=2020-04-26|title=Germany flips to Apple-Google approach on smartphone contact tracing|language=en|work=Reuters|url=https://uk.reuters.com/article/uk-health-coronavirus-europe-tech-idUKKCN22807X|access-date=2020-04-26}}</ref> followed shortly after by Ireland <ref>{{Cite news|url=https://www.irishtimes.com/business/technology/hse-covid-19-tracing-app-data-will-be-stored-on-individual-devices-1.4240304|title=HSE Covid-19 tracing app data will be stored on individual devices|date=2020-04-29|newspaper=The Irish Times|access-date=2020-05-06|language=en}}</ref> and Italy.<ref>{{Cite web|url=https://bylinetimes.com/2020/05/01/is-it-safe-the-immuni-app-digital-surveillance-during-the-coronavirus-pandemic/|title=Is it Safe? THE IMMUNI APP Digital Surveillance during the Coronavirus Pandemic|date=2020-05-01|work=Byline Times / La Stampa|access-date=2020-05-06|language=en}}</ref> Despite already adopting the centralised [[Software:BlueTrace|BlueTrace]] protocol,<ref>{{Cite web|title=Five questions we need answered about the government's coronavirus contact tracing app|url=https://www.abc.net.au/news/science/2020-04-17/5-questions-the-governments-coronavirus-contact-tracing-app/12151264|date=2020-04-16|website=ABC News|language=en-AU|access-date=2020-05-21}}</ref> Australia's Department of Health and Digital Transformation Agency were investigating whether the protocol could be implemented to overcome limitations of its [[Software:COVIDSafe|COVIDSafe]] app.<ref name=":2" /> On May 25, Switzerland became the first country to launch an app leveraging the protocol, SwissCovid, beginning with a small pilot group.<ref name=":10">{{cite web|date=25 May 2020|title=SwissCovid App startet in die Pilotphase|trans-title=SwissCovid app launched into pilot phase|url=https://www.bag.admin.ch/bag/de/home/das-bag/aktuell/medienmitteilungen.msg-id-79229.html|access-date=25 May 2020|language=de}}</ref>

In England, the National Health Service (NHS) trialed both an [[Software:NHS COVID-19|in-house app]] on a centralized platform developed by its NHSX division, and a second app using Exposure Notification.<ref>{{cite news|last1=Neville|first1=Sarah|last2=Bradshaw|first2=Tim|last3=Warrell|first3=Helen|title=UK starts to build second contact tracing app|url=https://www.ft.com/content/446df516-4ec5-4c06-b39f-dd89ea5f6f0b|access-date=8 May 2020|website=Financial Times|date=8 May 2020}}</ref> On June 18, the NHS announced that it would focus on using Exposure Notification to complement manual contact tracing, citing tests on the Isle of Wight showing that it had better cross-device compatibility (and would also be compatible with other European approaches), but that its distance calculations were not as reliable as the centralized version of the app,<ref>{{cite news|title=UK virus-tracing app switches to Apple-Google model|work=BBC News|date=18 June 2020|url=https://www.bbc.com/news/technology-53095336|access-date=2020-06-18}}</ref> an issue which was later rectified.<ref>{{cite arXiv|last1=Lovett|first1=Tom|last2=Briers|first2=Mark|last3=Charalambides|first3=Marcos|last4=Jersakova|first4=Radka|last5=Lomax|first5=James|last6=Holmes|first6=Chris|date=2020-07-09|title=Inferring proximity from Bluetooth Low Energy RSSI with Unscented Kalman Smoothers|class=eess.SP|eprint=2007.05057}}</ref><ref>{{Cite web|title=Updates to the algorithm underlying the NHS COVID-19 app|url=https://www.turing.ac.uk/blog/updates-algorithm-underlying-nhs-covid-19-app|access-date=2021-06-30|website=The Alan Turing Institute|language=en}}</ref> Later, it was stated that the app would be supplemented by [[QR code]]s at venues.<ref>{{Cite web|last=O'Halloran|first=Joe|date=July 31, 2020|title=UK contact-tracing app to be launched 'shortly' as Northern Ireland deploys service|url=https://www.computerweekly.com/news/252486951/UK-contact-tracing-app-to-be-launched-shortly-as-Northern-Ireland-deploys-service|access-date=2020-07-31|website=Computer Weekly|language=en}}</ref> A study of the impact of Exposure Notification in England and Wales estimated that it averted 8,700 (95% [[Confidence interval|confidence interval]] 4,700–13,500) deaths out of the 32,500 recorded from its introduction on 24 September 2020 to 31 December 2020.<ref>{{Cite journal|last1=Wymant|first1=Chris|last2=Ferretti|first2=Luca|last3=Tsallis|first3=Daphne|last4=Charalambides|first4=Marcos|last5=Abeler-Dörner|first5=Lucie|last6=Bonsall|first6=David|last7=Hinch|first7=Robert|last8=Kendall|first8=Michelle|last9=Milsom|first9=Luke|last10=Ayres|first10=Matthew|last11=Holmes|first11=Chris|date=2021-06-17|title=The epidemiological impact of the NHS COVID-19 app|journal=Nature|language=en|volume=594|issue=7863|pages=408–412|doi=10.1038/s41586-021-03606-z|pmid=33979832|bibcode=2021Natur.594..408W|s2cid=234484448|issn=0028-0836|doi-access=free}}</ref>

Canada launched its COVID Alert app, co-developed in partnership with [[Company:BlackBerry Limited|BlackBerry Limited]] and [[Company:Shopify|Shopify]],<ref>{{Cite web|date=2020-07-23|title=Here's a first look at the government's 'COVID Alert' contact tracing app|url=https://mobilesyrup.com/2020/07/23/heres-a-first-look-at-the-governments-covid-alert-contact-tracing-app/|access-date=2020-07-24|website=MobileSyrup|language=en}}</ref> on July 31 in Ontario.<ref name=":13" /> As of February 2022, only around 57,000 positive cases had been reported via the app, leading some critics to dismiss it as a failure.<ref name=":52">{{Cite web |date=2021-05-27 |title=Was Canada's COVID Alert app a hit or a miss? |url=https://www.ctvnews.ca/health/coronavirus/was-canada-s-covid-alert-app-a-hit-or-a-miss-1.5445730 |access-date=2022-05-07 |website=CTV News |language=en}}</ref><ref name=":72">{{Cite web |last=Nardi |first=Christopher |title=With low uptake, Canada 'gave up' on its COVID Alert app months ago, Newfoundland and Labrador health minister reveals in live update |url=https://www.saltwire.com/atlantic-canada/news/with-low-uptake-canada-gave-up-on-its-covid-alert-app-months-ago-newfoundland-and-labrador-health-minister-reveals-in-live-update-100675459/ |access-date=2022-05-07 |website= |publisher=SaltWire Network |language=en}}</ref><ref name=":42">{{Cite web |last=Turnbull |first=Sarah |date=2021-12-30 |title=COVID Alert app still active, but rarely used to record positive tests |url=https://www.ctvnews.ca/health/coronavirus/covid-alert-app-still-active-but-rarely-used-to-record-positive-tests-1.5723556 |url-status=live |archive-url=https://web.archive.org/web/20211230201100/https://www.ctvnews.ca/health/coronavirus/covid-alert-app-still-active-but-rarely-used-to-record-positive-tests-1.5723556 |archive-date=2021-12-30 |access-date=2022-01-02 |website=CTV News |language=en}}</ref>

In May 2020, Covid Watch launched the first calibration and beta testing pilot of the GAEN APIs in the United States at the University of Arizona.<ref>{{Cite web|url=https://www.kold.com/2020/05/28/ua-testing-app-trace-covid-cases-campus/|title=UA testing app to trace COVID-19 cases on campus|date=2020-05-28|website=KOLD News 13|language=en|access-date=2020-05-28}}</ref><ref>{{Cite web|url=https://tucson.com/news/local/education/college/online-apps-likely-to-play-a-big-role-in-rebooting-ua-campus-for-fall-semester/article_a7fe0f69-0db4-5f10-ad76-f6b1b4190ea7.html/|title=Online apps likely to play a big role in rebooting UA campus for fall semester|date=2020-05-28|website=Github|language=en|access-date=2020-05-28}}</ref> In Aug 2020, the app launched publicly for a phased roll-out in the state of Arizona.<ref name="news.arizona.edu">{{Cite web|date=2020-08-18|title=UArizona and Covid Watch Launch COVID-19 Exposure Notification App|url=https://news.arizona.edu/story/uarizona-and-covid-watch-launch-covid-19-exposure-notification-app|access-date=2020-08-20|website=University of Arizona News|language=en}}</ref><ref name="Covid Watch Arizona">{{Cite web|title=Covid Watch Arizona|url=https://apps.apple.com/us/app/covid-watch-arizona/id1521655110|access-date=2020-08-20|website=App Store|language=en-us}}</ref><ref name="play.google.com">{{Cite web|title=Covid Watch Arizona - Apps on Google Play|url=https://play.google.com/store/apps/details?id=gov.azdhs.covidwatch.android&hl=en_US|access-date=2020-08-20|website=play.google.com|language=en}}</ref>

The U.S. [[Organization:Association of Public Health Laboratories|Association of Public Health Laboratories]] (APHL) stated in July 2020 that it was working with Apple, Google, and [[Company:Microsoft|Microsoft]] on a national reporting server for use with the protocol, which it stated would ease adoption and interoperability between states.<ref>{{Cite web|date=2020-07-17|title=Bringing COVID-19 exposure notification to the public health community|url=https://www.aphlblog.org/bringing-covid-19-exposure-notification-to-the-public-health-community/|access-date=2020-09-01|website=APHL Lab Blog|language=en-US}}</ref><ref name=":15" />

In August 2020, Google stated that at least 20 U.S. states had expressed interest in using the protocol. In Alabama, the Alabama Department of Public Health, [[Organization:University of Alabama at Birmingham|University of Alabama at Birmingham]], and the [[Organization:University of Alabama System|University of Alabama System]] deployed the "GuideSafe" app for university students returning to campus, which includes Exposure Notification features.<ref name=":11">{{Cite web|last=Walsh|first=Lauren|date=2020-08-03|title=COVID-19 testing, monitoring system GuideSafe launches|url=https://abc3340.com/news/local/covid-19-testing-monitoring-system-guidesafe-launches|access-date=2020-08-05|website=ABC 33/40}}</ref><ref>{{Cite web|date=2020-08-03|title=Alabama launches contact tracing app based on Google-Apple API|url=https://statescoop.com/alabama-launches-contact-tracing-app-based-on-google-apple-api/|access-date=2020-08-06|website=StateScoop|language=en}}</ref> On August 5, the Virginia Department of Health released its "COVIDWise" app — making it the first U.S. state to release an Exposure Notification-based app for the general public.<ref>{{Cite web|title=Virginia Set To Release COVIDWISE App To Public This Week|url=https://vpm.org/news/articles/15373/virginia-set-to-release-covidwise-app-to-public-this-week|access-date=2020-08-05|website=VPM.org|date=2 August 2020 |language=en}}</ref><ref>{{Cite web|last=Wetsman|first=Nicole|date=2020-08-05|title=Apple and Google's COVID-19 tracking system will make its full US debut in new Virginia app|url=https://www.theverge.com/2020/8/5/21355500/virginia-apple-google-contact-tracing-app-covid-alabama|access-date=2020-08-05|website=The Verge|language=en}}</ref><ref name=":12">{{Cite news|title=Virginia Unveils App To Aid Contact Tracing|url=https://www.npr.org/sections/coronavirus-live-updates/2020/08/05/899414953/virginia-unveils-app-to-aid-contact-tracing|access-date=2020-08-06|website=NPR.org|language=en}}</ref> North Dakota and Wyoming released an EN app known as "Care19 Alert", developed by ProudCrowd and using the APHL server (the app is a spin-off from an existing location logging application it had developed, based on one it had developed primarily for use by students travelling to attend college football away games).<ref>{{Cite web|title=ND launches Care19 Alert app to help reduce spread of COVID-19|url=https://www.minotdailynews.com/news/local-news/2020/08/nd-launches-care19-alert-app-to-help-reduce-spread-of-covid-19/|access-date=2020-09-01|website=minotdailynews.com|language=en-US}}</ref><ref>{{Cite news|date=2020-08-14|title=Three more U.S. states launching coronavirus exposure warning apps|language=en|work=Reuters|url=https://ca.reuters.com/article/technologyNews/idCAKCN2592WR-OCATC|access-date=2020-09-01}}</ref>

Maryland, Nevada, Virginia, and Washington, D.C. have announced plans to use EN Express.<ref name=":15" /> In September, Delaware, New Jersey, New York, and Pennsylvania all adopted "COVID Alert" apps developed by NearForm, which are based on its [[Software:COVID Tracker Ireland|COVID Tracker Ireland]] app.<ref>{{Cite web|last=Goodin-Smith|first=Ellie Rushing, Oona|title=Contact tracing app tells Pennsylvanians if they've been exposed to coronavirus|url=https://www.inquirer.com/health/coronavirus/contact-tracing-app-pennsylvania-coronavirus-cases-20200923.html|access-date=2020-10-07|website=Philadelphia Inquirer|date=23 September 2020 |language=en-US}}</ref><ref name=":18">{{Cite web|last=Gorey|first=Colm|date=2020-10-02|title=NearForm contact-tracing apps launched in New York and New Jersey|url=https://www.siliconrepublic.com/enterprise/new-york-new-jersey-contact-tracing-apps-nearform|access-date=2020-10-07|website=Silicon Republic|language=en}}</ref> Later that month, the [[Organization:Norwegian Institute of Public Health|Norwegian Institute of Public Health]] announced that it would lead development of an Exposure Notification-based app for the country, which replaces a centralized app that had ceased operations in June 2020 after the Norwegian Data Protection Authority ruled that it violated privacy laws.<ref name=":19">{{Cite web|title=NIPH starts work on a new solution for digital contact tracing|url=https://www.fhi.no/en/news/2020/niph-starts-work-on-a-new-solution-for-digital-contact-tracing/|access-date=2020-11-17|website=Norwegian Institute of Public Health|language=en}}</ref><ref name=":20">{{Cite news|date=2020-10-21|title=Uden konkurrence: Netcompany vinder ordren på en ny norsk smittestop-app|url=https://www.computerworld.dk/art/253847/uden-konkurrence-netcompany-vinder-ordren-paa-en-ny-norsk-smittestop-app|access-date=2020-11-17|website=Computerworld|language=da}}</ref>

In Nov 2020, Bermuda launched the Wehealth Bermuda app developed by Wehealth, a Public Benefit Corporation, which was based on the Covid Watch app released in Arizona.<ref name=":26">{{Cite web|date=2020-11-24|title=The WeHealth Bermuda App Is Now Live|url=https://www.wehealth.org/news/wehealth-bermuda-app-is-now-live|access-date=2023-03-08|website=Wehealth News|language=en-US}}</ref><ref name=":27">{{Cite web |date=2020-11-24 |title=Wehealth Bermuda on the Play Store |url=https://play.google.com/store/apps/details?id=org.wehealth.exposure |access-date=2023-03-08 |website=Google Play Store |language=en-US}}</ref><ref name=":28">{{Cite web |date=2020-11-24 |title=Wehealth Bermuda on the App Store |url=https://apps.apple.com/us/app/wehealth-bermuda/id1535781209 |access-date=2023-03-08 |website=Apple App Store |language=en-US}}</ref>
{| class="wikitable sortable"
|+
!Country
!Region/State
!Name
! data-sort-type="date" |Announced/Released
! class="unsortable" |Notes
|-
| colspan="2" |{{Flagcountry|AUT}}
|Stopp Corona App
|June 26, 2020
|<ref>{{Cite web |url=https://www.roteskreuz.at/news/datum/2020/06/26/stopp-corona-app-das-update-fuer-den-automatischen-handshake-ist-da/ |title=Rotes Kreuz: Stopp Corona-App: Das Update für den automatischen Handshake ist da |access-date=2020-08-22 |archive-date=2020-10-23 |archive-url=https://web.archive.org/web/20201023022619/https://www.roteskreuz.at/news/datum/2020/06/26/stopp-corona-app-das-update-fuer-den-automatischen-handshake-ist-da/ |url-status=dead }}</ref>
|-
| colspan="2" |{{Flagcountry|BRA}}
|Coronavírus-SUS
|July 31, 2020
|<ref>{{cite news |title= Aplicativo Coronavírus-SUS vai alertar contatos próximos de pacientes com Covid-19 |url=http://www.saude.gov.br/noticias/agencia-saude/47292-aplicativo-coronavirus-sus-vai-alertar-contatos-proximos-de-pacientes-com-covid-19|access-date=31 July 2020 |language=pt-br |publisher=Ministério da Saúde |date=31 July 2020}}</ref>
|-
| colspan="2" |{{Flagcountry|Bermuda}}
|Wehealth Bermuda
|Nov 24, 2020
|<ref name=":26" /><ref name=":27" /><ref name=":28" />
|-

| colspan="2" |{{Flagcountry|BEL}}
|Coronalert
|October 1, 2020 (public)
|September 2, 2020 (Pilot phase)&nbsp;<ref>{{cite news |title= Coronalert", l'application de traçage belge devrait être disponible dès ce mois de septembre |url= https://www.rtbf.be/info/societe/detail_coronalert-l-application-de-tracage-digital-belge-devrait-etre-disponible-des-septembre?id=10573149 |access-date=27 September 2020 |language=fr-be |publisher=RTBF |date= 3 September 2020}}</ref>
|-
| colspan="2" |{{Flagcountry|CAN}}
|COVID Alert
| data-sort-value="July 31, 2020" |July 31, 2020
|Available in New Brunswick, Newfoundland and Labrador, Ontario, Manitoba, Saskatchewan, Quebec, Prince Edward Island, and Nova Scotia.<ref>{{Cite web|title=COVID Alert app now operational in Saskatchewan|url=https://www.ckom.com/2020/09/18/covid-alert-app-now-operational-in-saskatchewan/|access-date=2020-09-18|website=650 CKOM|language=en}}</ref><ref name=":13">{{Cite web|date=2020-07-31|title=New COVID-19 notification app rolls out in Ontario|url=https://www.cbc.ca/news/politics/covid-pandemic-app-ontario-1.5670239|access-date=2020-07-31|website=CBC News|language=en}}</ref><ref name=":17">{{Cite web|date=2020-10-06|title=Few provinces still resisting COVID Alert app as new features under consideration|url=https://www.cbc.ca/news/technology/covid-alert-app-features-coronavirus-quebec-1.5751497|access-date=2020-10-07|website=CBC News}}</ref> Alberta and British Columbia have declined its use.<ref name=":17" />
|-
| colspan="2" |{{Flagcountry|CZE}}
|eRouška (eMask)
|September 17, 2020
|Since version 2.1<ref>{{cite web |title=eRouška – chráním sebe, chráním tebe |url=https://erouska.cz/ |website=erouska.cz |access-date=18 September 2020 |language=cs}}</ref><ref>{{cite news|last1=Kůžel |first1=Filip |last2=Lutonský |first2=Marek |title=eRouška 2.0: Co to je, jak se používá a proč se nemusíte bát o soukromí |url=https://www.mobilmania.cz/clanky/erouska-20-co-to-je-jak-se-pouziva-a-proc-se-nemusite-bat-o-soukromi/sc-3-a-1349357/default.aspx |access-date=19 September 2020 |work=MobilMania.cz |language=cs}}</ref>
|-
| colspan="2" |{{Flagcountry|DEN}}
|Smittestop
|June 18, 2020
|<ref>{{cite web|date=2020-06-25|title=Smittestop appen downloadet tæt på en halv million gange på den første uge|url=http://sundhedsministeriet.dk/Aktuelt/Nyheder/Coronavirus/2020/Juni/Smittestop-appen-downloadet-taet-paa-en-halv-million-gange-paa-den-foerste-uge.aspx|publisher=Ministry of Health (Denmark)|language=da|access-date=2020-06-26|archive-date=2020-06-28|archive-url=https://web.archive.org/web/20200628232725/http://sundhedsministeriet.dk/Aktuelt/Nyheder/Coronavirus/2020/Juni/Smittestop-appen-downloadet-taet-paa-en-halv-million-gange-paa-den-foerste-uge.aspx|url-status=dead}}</ref>
|-
| colspan="2" |{{Flagcountry|Estonia}}
|Hoia
|August 20, 2020
|<ref>{{cite news |title= The Estonian coronavirus mobile application HOIA is now available for download |url=https://www.sm.ee/en/news/estonian-coronavirus-mobile-application-hoia-now-available-download|access-date=2021-09-08 |language=en |publisher=Estonian Ministry of Social Affairs |date=2020-08-20}}</ref>
|-
| colspan="2" |{{Flagcountry|Finland}}
|Koronavilkku
|August 31, 2020
|<ref>{{cite news |title= First peek: Finland's Covid-19 contact tracing app |url=https://yle.fi/uutiset/osasto/news/first_peek_finlands_covid-19_contact_tracing_app/11487870|access-date=11 August 2020 |language=en |publisher=Yle NEWS |date=11 August 2020}}</ref>
|-
| colspan="2" |{{Flagcountry|GER}}
|Corona-Warn-App
|June 16, 2020
|<ref>{{Cite web|last=Bundesregierung|title=Corona-Warn-App|url=https://www.bundesregierung.de/breg-de/themen/corona-warn-app|access-date=2020-06-16|language=de}}</ref>
|-
| colspan="2" |{{Flagcountry|GIB}}
|BEAT Covid Gibraltar
|June 18, 2020
|Based on [[Software:COVID Tracker Ireland|COVID Tracker Ireland]] and will interoperate with it.<ref name="bbc-20200910" /><ref name="beatcovid">{{cite web |url=https://www.gibraltar.gov.gi/press-releases/beat-covid-gibraltar-app-4092020-5976 |title=Beat Covid Gibraltar App - 409/2020 |publisher=HM Government of Gibraltar |date=18 June 2020}}</ref>
|-
| colspan="2" |{{ISL}}
|Rakning C-19
|May 12, 2021
|GEAN implementation activated in May 2021, replaced previous version of app which used GPS tracking stored on-device launched in April 2020.<ref>{{Cite web |last=Þórhallsson |first=Markús Þ |date=2021-05-12 |title=Uppfærslan auðveldar rakningu þegar tengsl eru óþekkt - RÚV.is |url=https://www.ruv.is/frettir/innlent/2021-05-12-uppfaerslan-audveldar-rakningu-thegar-tengsl-eru-othekkt/ |access-date=2023-03-06 |website=RÚV}}</ref><ref>{{Cite web |title=Nearly 40% of Icelanders are using a covid app—and it hasn't helped much |url=https://www.technologyreview.com/2020/05/11/1001541/iceland-rakning-c19-covid-contact-tracing/ |access-date=2023-03-06 |website=MIT Technology Review |language=en}}</ref>
|-
| colspan="2" |{{Flagcountry|IRL}}
|[[Software:COVID Tracker Ireland|COVID Tracker Ireland]]
|July 7, 2020
|<ref>{{cite news|url=https://www.irishtimes.com/news/health/coronavirus-hse-reports-725-000-downloads-of-new-contact-tracing-app-since-launch-1.4298165|title=Coronavirus: HSE reports 725,000 downloads of new contact-tracing app since launch|publisher=The Irish Times|first1=Martin|last1=Wall|first2=Ciara|last2=O'Brien|first3=Mark|last3=Hilliard|date=7 July 2020|access-date=9 July 2020}}</ref><ref name="bbc-20200730">{{cite news |url=https://www.bbc.co.uk/news/uk-northern-ireland-53599514 |title=Covid-19: Tracing app is released for NI |work=BBC News |date=30 July 2020 |access-date=31 July 2020}}</ref>
|-
| colspan="2" |{{Flagcountry|ITA}}
|Immuni
|June 1, 2020
|<ref>{{cite news|date=1 June 2020|title=Italy launches COVID-19 contact-tracing app amid privacy concerns|work=Reuters|url=https://www.reuters.com/article/us-health-coronavirus-italy-app/italy-launches-covid-19-contact-tracing-app-amid-privacy-concerns-idUSKBN2383EW|access-date=3 June 2020}}</ref>
|-
| colspan="2" |{{Flagcountry|JPN}}
|COCOA
|June 19, 2020
|<ref>{{cite web|last=Byford|first=Sam|date=2020-06-19|title=Japan rolls out Microsoft-developed COVID-19 contact tracing app|url=https://www.theverge.com/2020/6/19/21296603/japan-covid-19-contact-tracking-app-cocoa-released|access-date=2020-06-20|website=The Verge|language=en}}</ref>
|-
| colspan="2" |{{Flagcountry|JER}}
|Jersey COVID Alert
|September 21, 2020
|<ref>{{Cite web|last=Jersey|first=States of|title=Government of Jersey|url=http://www.gov.je/Health/Coronavirus/CovidAlert/Pages/JerseyCOVIDAlertAppTermsofUse.aspx|access-date=2020-10-07|website=Gov.je|language=en}}</ref>
|-
| colspan="2" |{{Flagcountry|LAT}}
|Apturi Covid
|May 29, 2020
|<ref>{{cite web|title=Latvian 'Stop Covid' app first of its kind in the world|url=https://eng.lsm.lv/article/society/health/latvian-stop-covid-app-first-of-its-kind-in-the-world.a361746/|access-date=2020-05-20|website=Lsm.lv|language=en}}</ref>
|-
| colspan="2" |{{Flagcountry|LBN}}
|Ma3an
|July 16, 2020
|<ref>{{Cite web|url=http://www.moph.gov.lb/|title=moph|website=Moph.gov.lb|access-date=27 June 2022}}</ref>
|-
| colspan="2" |{{Flagicon|Netherlands}} Netherlands
|CoronaMelder
|October 10, 2020 (full release)
|<ref>{{Cite web|url=https://coronamelder.nl/en|title = Stop the spread of the coronavirus, download |website=Coronamelder.nl}}</ref>
|-
| colspan="2" |{{Flagicon|NZL}} [[Earth:New Zealand|New Zealand]]
|NZ COVID Tracer
|December 10, 2020 (full release)
|<ref>{{Cite web|url=https://www.health.govt.nz/our-work/diseases-and-conditions/covid-19-novel-coronavirus/covid-19-resources-and-tools/nz-covid-tracer-app/how-nz-covid-tracer-works/bluetooth-tracing|title = Bluetooth tracing|website=Health.govt.nz| date=15 August 2023 }}</ref>
|-
| colspan="2" |{{Flagcountry|NOR}}
|Smittestopp
|December 21, 2020
|Replaced a version of the app that was suspended earlier in the year due to scrutiny from the local Norwegian Data Protection Authority.<ref name=":19" /><ref name=":20" />
|-
| colspan="2" |{{Flagcountry|PHL}}
|[[Software:StaySafe.ph|StaySafe.ph]]
|March 29, 2021
|GAEN implementation activated in April 2021 <ref>{{cite news|last=Ranada|first=Pia|date=2 April 2021|title=StaySafe to use Google Apple Exposure Notifications for contact tracing|work=Rappler|url=https://www.rappler.com/nation/staysafe-to-use-google-apple-exposure-notifications-for-contact-tracing|access-date=27 June 2021}}</ref>
|-
| colspan="2" |{{Flagcountry|POL}}
|ProteGO Safe
|June 9, 2020
|Update to existing encounter logging app.<ref>{{cite news|date=9 June 2020|title=Ministerstwo cyfryzacji uruchomilo aplikacje protego safe do sledzenia koronawirusa|language=pl|work=Wirtualna Polska|url=https://tech.wp.pl/ministerstwo-cyfryzacji-uruchomilo-aplikacje-protego-safe-do-sledzenia-koronawirusa-6519587260446337a|access-date=9 June 2020}}</ref>
|-
| colspan="2" |{{Flagcountry|POR}}
|STAYAWAY COVID
|August 28, 2020
|<ref>{{cite news| title=App portuguesa de rastreio à Covid-19 já está disponível em Android e iOS |url=https://observador.pt/2020/08/28/app-portuguesa-de-rastreio-a-covid-19-ja-esta-disponivel-em-android/|language=pt|date=28 August 2020|access-date=29 August 2020|website=Observador}}</ref>
|-
| colspan="2" |{{Flag|Russia}}
|Gosuslugi. Covid Tracker
|November 23, 2020
|https://play.google.com/store/apps/details?id=com.minsvyaz.gosuslugi.exposurenotificationdroid
|-
| colspan="2" |{{Flagcountry|RSA}}
|COVID Alert SA
|September 1, 2020
|<ref>{{cite web|title=Download the app – Every COVID Alert SA app download means more lives saved in SA|url=https://sacoronavirus.co.za/2020/09/01/download-the-app-every-covid-alert-sa-app-download-means-more-lives-saved-in-sa/|access-date=2020-09-19|website=SAcoronavirus.co.za|date=September 2020|language=en}}</ref>
|-
| colspan="2" |{{Flagcountry|SPA}}
|Radar COVID
| data-sort-value="June 30, 2020" |June 30, 2020 (beta test)
|<ref>{{Cite web|last=Pérez|first=Enrique|date=2020-06-30|title=Probamos Radar COVID: así funciona la aplicación de rastreo de contactos que usaremos en España|url=https://www.xataka.com/aplicaciones/probamos-radar-covid-asi-funciona-aplicacion-rastreo-contactos-que-usaremos-espana|access-date=2020-07-28|website=Xataka|language=es}}</ref>
|-
| colspan="2" |{{Flagcountry|SUI}}
|SwissCovid
|May 26, 2020 (pilot phase)
|<ref name=":10" />
|-
|-
| colspan="2" |{{Flagcountry|TWN}}
|臺灣社交距離
|May 3, 2021
|<ref>{{Cite web|date=2021-05-03|title=臺灣社交距離App |url=https://www.cdc.gov.tw/Category/Page/R8bAd_yiVi22CIr73qM2yw|website=Taiwan Centers for Disease Control|access-date=2021-05-03}}</ref>
|-
| colspan="2" |{{Flagcountry|THA}}
|Thai Covid Alert
|April 26, 2022
|<ref>{{Cite web|date=2022-04-26|title=วิธีเปิดการแจ้งเตือนการสัมผัสเชื้อโควิด-19 บน iPhone|url=https://www.iphonemod.net/iphone-covid-19-notification-how-to.html|website=iMod|access-date=2022-04-27}}</ref>
|-
| rowspan="3" |{{Flagcountry|United Kingdom}}
|{{Flagcountry|ENG}}<br />{{Flagcountry|WAL}}
|[[Software:NHS COVID-19|NHS COVID-19]]
|September 24, 2020
|<ref name=":51">{{cite news|date=24 September 2020|title=NHS Covid-19 app: England and Wales get smartphone contact tracing for over-16s|language=en|website=BBC|url=https://www.bbc.co.uk/news/technology-54270334|access-date=24 September 2020}}</ref>
|-
|{{Flagcountry|Northern Ireland|union}}
|StopCOVID NI
|July 30, 2020
|Interoperates with [[Software:COVID Tracker Ireland|COVID Tracker Ireland]].<ref name="bbc-20200730" />
|-
|[[File:Flag of Scotland.svg|link=Scotland|alt=Scotland|23x23px]] Scotland
|Protect Scotland
|September 11, 2020
|Based on [[Software:COVID Tracker Ireland|COVID Tracker Ireland]] and will interoperate with it.<ref name="bbc-20200910">{{cite news |url=https://www.bbc.co.uk/news/uk-scotland-54071100 |title=Scotland's new tracing app: What you need to know about Protect Scotland |work=BBC News |date=10 September 2020 |access-date=11 September 2020}}</ref>
|-
| rowspan="25" |{{Flagicon|United States}} {{wipe|United States}}
|{{Flagicon|Alabama}} Alabama
|GuideSafe
|August 3, 2020
|Targeting [[Organization:University of Alabama System|University of Alabama]] students as part of a larger program under the same name.<ref name=":11" />
|-
|{{Flagicon|Alaska}} [[Earth:Alaska|Alaska]]
|Alaska COVID ENX
|January 20, 2022
|<ref>{{Cite web |title=Alaska ENX {{!}} University of Alaska Anchorage {{!}} University of Alaska Anchorage |url=https://www.uaa.alaska.edu/alaskaenx/index.cshtml |access-date=2022-03-28 |website=Uaa.alaska.edu}}</ref>
|-
|{{Flagicon|Arizona}} Arizona
|Covid Watch
|May 28, 2020 (attenuation and dynamic risk testing)
August 19, 2020 (released)
|Targeting [[Organization:University of Arizona|University of Arizona]] in a phased roll-out for the state of Arizona.<ref name="news.arizona.edu" /><ref name="Covid Watch Arizona" /><ref name="play.google.com" />
|-
|{{Flagicon|California}} {{wipe|California}}
|CA Notify
|December 10, 2020
|<ref name=":22">{{Cite web|date=2020-12-29|title=CA Notify app offers COVID-19 exposure alerts for Stanford community|url=https://www.stanforddaily.com/2020/12/28/ca-notify-app-offers-covid-19-exposure-alerts-for-stanford-community/|access-date=2021-01-13|website=The Stanford Daily}}</ref><ref name=":23">{{Cite web|date=2020-12-15|title=More than 6 million have signed up for California's COVID-19 alert system|url=https://www.sandiegouniontribune.com/news/health/story/2020-12-14/more-than-6-million-californians-have-signed-up-for-smartphone-covid-19-alert-system|archive-url=|archive-date=|access-date=2021-01-13|website=San Diego Union-Tribune|language=en-US}}</ref>
|-
|{{Flagicon|Colorado}} Colorado
|CO Exposure Notifications
|October 25, 2020
|<ref>{{Cite web|url=https://www.addyourphone.com/|title=CO Exposure Notifications|website=Addyourphone.com|access-date=27 June 2022}}</ref>
|-
|{{Flagicon|Connecticut}} Connecticut
|COVID Alert CT
|November 12, 2020
|<ref>{{Cite web|title=COVID-19 Exposure Notifications Now Available on Your Phone|url=https://www.nbcconnecticut.com/news/local/covid-19-exposure-notifications-now-available-on-your-phone/2359071/|access-date=2020-11-17|website=NBC Connecticut|date=12 November 2020 |language=en-US}}</ref>
|-
|{{Flagicon|Delaware}} Delaware
|COVID Alert DE
|September 15, 2020
|Based on [[Software:COVID Tracker Ireland|COVID Tracker Ireland]].<ref name=":18" />
|-
|{{Flagicon|Guam}} Guam
|Guam Covid Alert
|September 10, 2020
|Based on the PathCheck Foundation's GAEN Mobile project
|-
|{{Flagicon|Hawaii}} Hawaii
|Aloha Safe Alert
|November 11, 2020
|Based on the PathCheck Foundation's GAEN Mobile project
|-
|{{Flagicon|Louisiana}} Louisiana
|COVID Defense
|January 22, 2021
|Based on the PathCheck Foundation's GAEN Mobile project&nbsp;<ref>{{Cite web|url=https://ldh.la.gov/news/5997|title=In response to third COVID surge, Louisiana launches COVID Defense &#124; La Dept. of Health|website=Ldh.la.gov|access-date=27 June 2022}}</ref><ref>{{Cite web|url=https://www.coviddefensela.com/|title=COVID Defense - Louisiana's Smartphone App|website=Coviddefensela.com|access-date=27 June 2022}}</ref>
|-
|{{Flagicon|Maryland}} Maryland
|MD COVID Alert
|October 10, 2020
|<ref>{{Cite web|title=Maryland Department of Health launches MD COVID Alert|url=https://health.maryland.gov/newsroom/Pages/Maryland-Department-of-Health-launches-MD-COVID-Alert.aspx|access-date=2020-11-10|website=health.maryland.gov}}</ref>
|-
|{{Flagicon|Massachusetts}}{{wipe|Massachusetts}}
|MassNotify
|
|Uses EN Express.<ref>{{Cite web|last=Wetsman|first=Nicole|date=2021-06-21|title=Massachusetts' COVID-19 exposure notification app auto-installed on Android phones|url=https://www.theverge.com/2021/6/21/22543486/massnotify-covid-exposure-android-google-apple|access-date=2021-06-21|website=The Verge|language=en}}</ref>
|-
|{{Flagicon|Michigan}} Michigan
|MI COVID Alert
|October 15, 2020 ([[Organization:Michigan State University|Michigan State University]] pilot)
November 9, 2020 (statewide)
|<ref>{{Cite web|title=Spartans Respond with MI COVID Alert|url=https://msu.edu/together-we-will/mi-covid-alert/2020-11-09-update.html|access-date=2020-11-10|website=msu.edu}}</ref><ref>{{Cite web|title=Coronavirus - MDHHS and DTMB Roll Out COVID-19 Exposure Alert App Statewide|url=https://www.michigan.gov/coronavirus/0,9753,7-406-98158-544803--,00.html|access-date=2020-11-10|website=Michigan.gov}}</ref><ref>{{Cite web|last=Shamus|first=Kristen Jordan|title=Michigan rolls out new app to alert people of COVID-19 exposure|url=https://www.freep.com/story/news/health/2020/11/09/michigan-rolls-out-new-app-alert-people-covid-19-exposure/6220013002/|access-date=2020-11-10|website=Detroit Free Press|language=en-US}}</ref>
|-
|{{Flagicon|Minnesota}} Minnesota
|COVIDaware MN
|November 23, 2020
|<ref>{{Cite web|title=COVIDaware MN: Minnesota's free COVID-19 exposure notification app|url=https://mn.gov/covid19/for-minnesotans/covidawaremn/index.jsp|access-date=2020-11-26|website=mn.gov|language=en-US}}</ref><ref>{{Cite web|title=Minnesota rolls out new app for COVID exposure alerts|url=https://www.mprnews.org/story/2020/11/23/walz-to-announce-technology-to-help-spread-slow-of-covid19|access-date=2020-11-26|website=Mprnews.org|date=23 November 2020 |language=en-US}}</ref>
|-
|{{Flagicon|Missouri}} Missouri
|MO/Notify
|July 29, 2021
|Targeting [[Organization:Washington University in St. Louis|Washington University in St. Louis]] in a phased roll-out for the state of Missouri.<ref>{{Cite web|title=COVID-19 Exposure Notifications system launches for university community|url=https://medicine.wustl.edu/news/covid-19-exposure-notifications-system-launches-for-university-community/|access-date=2021-08-24|website=medicine.wustl.edu|date=29 July 2021|language=en-US}}</ref><ref>{{Cite web|title=MO/Notify|url=https://play.google.com/store/apps/details?id=gov.mo.covid19.exposurenotifications|access-date=2021-08-24|website=play.google.com|language=en-US}}</ref>
|-
|{{Flagicon|New Jersey}} New Jersey
|COVID Alert NJ
|September 30, 2020
|Based on [[Software:COVID Tracker Ireland|COVID Tracker Ireland]].<ref name=":18" />
|-
|{{Flagicon|New York}} New York
|COVID Alert NY
|September 30, 2020
|Based on [[Software:COVID Tracker Ireland|COVID Tracker Ireland]].<ref name=":18" />
|-
|{{Flagicon|North Carolina}} North Carolina
|SlowCOVIDNC
|September 22, 2020
|The app was shut down on or before August 19, 2022.<ref>{{Cite web |date= |title=SlowCOVIDNC app {{!}} NC COVID-19 |url=https://covid19.ncdhhs.gov/about-covid-19/slow-spread/slowcovidnc-app |url-status=live |archive-url=https://web.archive.org/web/20220819183424/https://covid19.ncdhhs.gov/about-covid-19/slow-spread/slowcovidnc-app |archive-date=2022-08-19 |access-date=2022-10-18 }}</ref>
|-
|{{Flagicon|North Dakota}} North Dakota
|Care19 Alert
|August 13, 2020
|<ref>{{cite web|title=North Dakota announces launch of Care19 Alert app to help reduce spread of COVID-19 as students return|url=https://www.governor.nd.gov/news/north-dakota-announces-launch-care19-alert-app-help-reduce-spread-covid-19-students-return|access-date=2020-08-13|publisher=ND Office of the Governor}}</ref>
|-
|{{Flagicon|Pennsylvania}} Pennsylvania
|COVID Alert PA
|September 24, 2020
|Based on [[Software:COVID Tracker Ireland|COVID Tracker Ireland]].<ref name=":18" />
|-
|{{Flagicon|Utah}} Utah
|UT Exposure Notifications
|February 16, 2021
|<ref>{{cite web|title=Google/Apple Exposure Notification Express Launches in Utah|url=https://coronavirus.utah.gov/google-apple-exposure-notification-express-launches-in-utah/|access-date=2021-02-17|publisher=UT Department of Health}}</ref>
|-
|{{Flagicon|Virginia}} Virginia
|COVIDWise
|August 5, 2020
|<ref name=":12" />
|-
|{{Flagicon|Washington}} {{wipe|Washington (state)}}
|WA Notify
|November 30, 2020
|<ref>{{cite web|title=WA Notify system goes live with COVID exposure notifications for iPhone and Android users in Washington state|url=https://www.seattletimes.com/seattle-news/health/wa-notify-system-goes-live-with-covid-exposure-notifications-for-iphone-users-in-washington-state | date=2020-11-30 |publisher=The Seattle Times}}</ref><ref>{{cite web|title=Washington Exposure Notifications - WA Notify|url=https://www.doh.wa.gov/Emergencies/COVID19/WANotify|date=2020-11-30|access-date=2020-11-30|publisher=Washington State Department of Health}}</ref>
|-
|{{Flagicon|Wisconsin}} Wisconsin
|WI Exposure Notification
|December 23, 2020
|<ref>{{cite web|title=COVID-19 Contact Tracing App Launches in Wisconsin|url=https://www.dhs.wisconsin.gov/news/releases/122320.htm|date=2020-12-23|publisher=Wisconsin Department of Health Services}}</ref>
|-
|{{Flagicon|Wyoming}} Wyoming
|Care19 Alert
|August 14, 2020
|<ref>{{cite web|title=Care19 Contact Tracing Apps|url=https://covid19.wyo.gov/care19-app|publisher=Wyoming COVID-19 Information}}</ref>
|-
| colspan="2" |{{Flagcountry|URY}}
|Coronavirus UY
|June 15, 2020
|<ref>{{cite news |title= Información sobre aplicación Coronavirus UY |url=https://www.gub.uy/ministerio-salud-publica/politicas-y-gestion/informacion-sobre-aplicacion-coronavirus|access-date=15 June 2020 |language=es |publisher=gub.uy |date=15 June 2020}}</ref>
|}

=== Alternatives ===
Some countries, such as France, have pursued centralized approaches to digital contact tracing, in order to maintain records of personal information that can be used to assist in investigating cases.<ref name=":6" /><ref>{{Cite news|last=Kelion|first=Leo|date=2020-05-20|title=Apple and Google's Covid-19 'watershed moment'|language=en-GB|work=BBC News|url=https://www.bbc.com/news/technology-52740131|access-date=2020-05-21}}</ref>  The French government asked Apple in April 2020 to allow apps to perform Bluetooth operations in the background, which would allow the government to create its own system independent of Exposure Notification.<ref>{{Cite news|last=Fouquet|first=Helene|date=20 April 2020|title=France Says Apple Bluetooth Policy Is Blocking Virus Tracker|url=https://www.bloomberg.com/news/articles/2020-04-20/france-says-apple-s-bluetooth-policy-is-blocking-virus-tracker|access-date=27 April 2020|newspaper=Bloomberg.com}}</ref>

On August 9, the Canadian province of Alberta announced plans to migrate to the EN-based COVID Alert from its BlueTrace-based ABTraceTogether app.<ref name=":16">{{Cite web|title=Alberta to adopt national COVID-19 tracing app|url=https://edmontonjournal.com/news/politics/alberta-to-adopt-national-covid-19-tracing-app|access-date=2020-08-09|website=Edmonton Journal|language=en-CA}}</ref><ref>{{Cite web|title=Alberta's contact-tracing app only works on iOS when phone is unlocked, app running in foreground|url=https://globalnews.ca/news/6898691/ab-trace-together-contact-app-alberta-covid-ios/|access-date=2020-08-09|website=Global News|language=en-US}}</ref> This did not occur, and on November 6 Premier of Alberta Jason Kenney announced that the province would not do so, arguing that ABTraceTogether was "from our view, simply a better and more effective public health tool", and that they would be required to phase out ABTraceTogether if they did switch.<ref name=":21">{{Cite web|last=Franklin|first=Michael|date=2020-11-06|title=Alberta will not adopt national COVID-19 Alert app: Kenney|url=https://calgary.ctvnews.ca/alberta-will-not-adopt-national-covid-19-alert-app-kenney-1.5178790|access-date=2020-11-17|website=CTV News Calgary|language=en}}</ref> British Columbia has also declined to adopt COVID Alert, with provincial health officer Bonnie Henry stating that COVID Alert was too "non-specific".<ref name=":21" />

Australia's officials have stated its [[Software:COVIDSafe|COVIDSafe]], which is based on Singapore's [[Software:BlueTrace|BlueTrace]], will not be shifting from manual intervention.<ref>{{Cite web|last=Grubb|first=Ben|date=2020-06-28|title='There's no way we're shifting': Australia rules out Apple-Google coronavirus tracing method|url=https://www.smh.com.au/technology/there-s-no-way-we-re-shifting-australia-rules-out-apple-google-coronavirus-tracing-method-20200629-p5573s.html|access-date=2020-09-23|website=The Sydney Morning Herald|language=en}}</ref><ref>{{Cite web|title=Apple/Google privacy preserving COVID-19 contact tracing. · Issue #10 · AU-COVIDSafe/mobile-ios|url=https://github.com/AU-COVIDSafe/mobile-ios/issues/10|access-date=2020-09-23|website=GitHub|language=en}}</ref>

In the United States, states such as California and Massachusetts declined to use the technology, opting for manual contact tracing.<ref>{{Cite magazine |title=Health Officials Say 'No Thanks' to Contact-Tracing Tech |url=https://www.wired.com/story/health-officials-no-thanks-contact-tracing-tech/ |last1=Volgelstein |first1=Fred |last2=Knight |first2=Will |date=2020-05-08 |magazine=Wired |language=en |access-date=2020-05-10}}</ref> California later reversed course and adopted the system in December 2020.<ref name=":22" /><ref name=":23" />

Chinese vendor [[Company:Huawei|Huawei]] (which cannot include Google software on its current Android products due to U.S. sanctions) added a OS-level DP-3T API known as "Contact Shield" to its Huawei Mobile Services stack in June 2020, which the company states is intended to be interoperable with Exposure Notification.<ref>{{Cite web|date=2020-06-08|title=Huawei releases its "Contact Shield" API for COVID-19 contact tracing|url=https://www.xda-developers.com/huawei-hms-core-contact-shield-api-covid-19-contact-tracing/|access-date=2020-10-07|website=xda-developers|language=en-US}}</ref>

== References ==
{{Reflist}}

== External links ==
* [https://www.google.com/covid19/exposurenotifications/ Official website] (Google)
* [https://developer.apple.com/exposure-notification/ Official website] (Apple)
* [https://www.apple.com/newsroom/2020/04/apple-and-google-partner-on-covid-19-contact-tracing-technology/ Announcement] (Apple)
* [https://blog.google/documents/57/Overview_of_COVID-19_Contact_Tracing_Using_BLE.pdf Overview presentation] (Google)
* [https://www.apple.com/covid19/contacttracing/ Technical specifications] (Apple)
* [https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FAQv1.0.pdf Exposure Notification: Frequently Asked Questions] {{Webarchive|url=https://web.archive.org/web/20200426210251/https://covid19-static.cdn-apple.com/applications/covid19/current/static/contact-tracing/pdf/ExposureNotification-FAQv1.0.pdf |date=2020-04-26 }} (Apple/Google)


[[Category:Google software]]
[[Category:Mobile applications]]

{{Sourceattribution|Exposure Notification}}