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{{short description|Unique code assigned for identification of a single unit}}
[[File:Seriennummer.JPG|thumb|alt=The serial number Y0139836 printed on an identity document|Serial number from an identity document]]
[[File:Travelers Cheques of 50 USD each issued by American Express, bought ca. 2012, showing incremental serial numbering.jpg|thumb|[[Traveller's cheque]]s, a kind of insured cash money in form of a paper cheque, are sold to customers in sets having ''consecutive'' numbers - one of the very few type of items where consumers have access to "serialized" similar things.]]

A '''serial number''' ('''SN''') is a [[Unique identifier|unique identifier]] used to ''uniquely'' identify an item, and is usually assigned incrementally or sequentially.

Despite being called serial "numbers", they do not need to be strictly numerical and may contain letters and other typographical symbols, or may consist entirely of a [[Character (computing)|character]] [[String (computer science)|string]].
==Applications of serial numbering==
[[File:NumeroPistola.JPG|thumb|Serial number on a Ballester–Molina [[Engineering:Semi-automatic pistol|semi-automatic pistol]]]]
{{details|Numbering scheme}}
Serial numbers identify otherwise identical individual units, thereby serving various practical uses. Serial numbers are a deterrent against theft and counterfeit products, as they can be recorded, and stolen or otherwise irregular goods can be identified. [[Engineering:Banknote|Banknote]]s and other transferable documents of value bear serial numbers to assist in preventing counterfeiting and tracing stolen ones. 

They are valuable in [[Quality control|quality control]], as once a defect is found in the production of a particular batch of product, the serial number will identify which units are affected. Some items with serial numbers are [[Vehicle identification number|automobiles]], [[Gun serial number|firearms]], electronics, and appliances.

==Smartphones and other smart devices==
[[File:TMP246M-M-352F serial number 20170608.jpg|thumb|Serial number of a [[laptop]] computer]] In [[Engineering:Smartphone|smartphone]]s, serial numbers are extended to the integrated [[Engineering:Electronic component|components]] in addition to the electronic device as a whole, also known as serialization. This gives unique individual parts such as the screen, battery, chip and camera a separate serial number. This is queried by the software for proper release for use.This practice by manufacturers limits the ''serial '''number''''' electronic devices.

===Serial numbers for intangible goods===
Serial numbers may be used to identify individual physical or intangible objects; for example, computer software or the right to play an online multiplayer game. The purpose and application is different. A software serial number, otherwise called a product key, is usually not embedded in the software but is assigned to a specific user with a [[Software license|right to use]] the software. The software will function only if a potential user enters a valid product code. The vast majority of possible codes are rejected by the software. If an unauthorized user is found to be using the software, the legitimate user can be identified from the code. It is usually not impossible, however, for an unauthorized user to create a valid but unallocated code either by trying many possible codes, or [[Reverse engineering|reverse engineering]] the software; use of unallocated codes can be monitored if the software makes an [[Internet]] connection.

==Other uses of the term==
The term ''serial number'' is sometimes used for codes which do not identify a single instance of something. For example, the [[International Standard Serial Number]] or ISSN used on magazines, journals and other [[Periodical literature|periodicals]], an equivalent to the [[International Standard Book Number]] (ISBN) applied to books, is assigned to each ''periodical''. It takes its name from the [[Social:Library science|library science]] use of the word ''serial'' to mean a periodical.

Certificates and [[Certificate authority|certificate authorities]] (CA) are necessary for widespread use of [[Cryptography|cryptography]]. These depend on applying mathematically rigorous serial numbers and serial number arithmetic, again not identifying a single instance of the content being protected.

[[File:Short_SC.1.jpg|thumb|The Royal Air Force (RAF) serial (''XG900'') on the [[Engineering:Short SC.1|Short SC.1]]]]

===Military and government use===
The term ''serial number'' is also used in military formations as an alternative to the expression ''[[Service number|service number]]''. In air forces, the serial number is used to uniquely identify individual aircraft and is usually painted on both sides of the aircraft fuselage, most often in the tail area, although in some cases the serial is painted on the side of the aircraft's fin/rudder(s). Because of this, the serial number is sometimes called a ''tail number''.

In the UK Royal Air Force (RAF) the individual serial takes the form of two letters followed by three digits, e.g., ''BT308''—the prototype [[Engineering:Avro Lancaster|Avro Lancaster]], or ''XS903''—an [[Engineering:English Electric Lightning|English Electric Lightning F.6]] at one time based at RAF Binbrook.<ref>{{cite web|url=http://1000aircraftphotos.com/Contributions/DentonNeville/6467.htm|title=British Aircraft Corporation Lightning F.Mk.6|website=1000aircraftphotos.com|access-date=2 June 2007|archive-date=29 September 2007|archive-url=https://web.archive.org/web/20070929084235/http://1000aircraftphotos.com/Contributions/DentonNeville/6467.htm|url-status=live}}</ref> During the [[Social:World War II|Second World War]] RAF aircraft that were secret or carrying secret equipment had "/G" (for "Guard") appended to the serial, denoting that the aircraft was to have an armed guard at all times while on the ground, e.g., ''LZ548/G''—the prototype [[Engineering:De Havilland Vampire|de Havilland Vampire]] [[Engineering:Jet engine|jet]] fighter, or ''ML926/G''—a [[Engineering:De Havilland Mosquito|de Havilland Mosquito XVI]] experimentally fitted with H2S radar. Prior to this scheme the RAF, and predecessor Royal Flying Corps (RFC), utilized a serial consisting of a letter followed by four figures, e.g., ''D8096''—a [[Engineering:Bristol F.2 Fighter|Bristol F.2 Fighter]] currently owned by the Shuttleworth Collection, or ''K5054''—the prototype [[Engineering:Supermarine Spitfire|Supermarine Spitfire]]. The serial number follows the aircraft throughout its period of service.

In 2009, the U.S. FDA published draft guidance for the [[Medicine:Pharmaceutical industry|pharmaceutical industry]] to use serial numbers on prescription drug packages.<ref name=giss>{{cite web|last=Food and Drug Administration |title=Guidance for Industry Standards for Securing the Drug Supply Chain - Standardized Numerical Identification for Prescription Drug Packages Draft Guidance |website=[[Organization:Food and Drug Administration|Food and Drug Administration]] |url=https://www.fda.gov/oc/guidance/drugsupplychain.html |access-date=19 April 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090511135327/https://www.fda.gov/oc/guidance/drugsupplychain.html |archive-date=11 May 2009 }}</ref>  This measure is intended to enhance the [[Traceability|traceability]] of drugs and to help prevent [[Medicine:Counterfeit medications|counterfeiting]]. The FDA also required a serial number or lot number to be added to [[Unsolved:Breast implant|breast implant]]s.<ref>{{cite web | url=https://www.mbcalliance.org/guestblogposts/force-content/stronger-guidance-about-breast-implant-safety/ | title=Stronger guidance about breast implant safety | date=14 December 2021 }}</ref>

==Serial number arithmetic==
Serial numbers are often used in network protocols. However, most sequence numbers in computer protocols are limited to a fixed number of bits, and will [[Arithmetic overflow|wrap around]] after sufficiently many numbers have been allocated. Thus, recently allocated serial numbers may duplicate very old serial numbers, but not other recently allocated serial numbers. To avoid ambiguity with these non-unique numbers, {{IETF RFC|1982}} "Serial Number Arithmetic", defines special rules for calculations involving these kinds of serial numbers.

[[Lollipop sequence numbering|Lollipop sequence number space]]s are a more recent and sophisticated scheme for dealing with finite-sized sequence numbers in protocols.

==See also==
{{div col}}
*{{annotated link|Engineering:Engine number}}
*{{annotated link|English numerals}}
*{{annotated link|Numbering scheme}}
*{{annotated link|Part number}}
*{{annotated link|SQL}} (serial identifiers for databases)
*{{annotated link|Vehicle identification number}}
*{{annotated link|Arithmometer}} – one of the first machines to sport a unique serial number
{{div col end}}

== Sources ==
*Elz, R., and R. Bush, {{IETF RFC|1982}} "Serial Number Arithmetic", Network Working Group, August 1996.
*Plummer, William W. [http://www.isi.edu/in-notes/ien/ien74.txt "Sequence Number Arithmetic"] {{Webarchive|url=https://web.archive.org/web/20081221213405/http://www.isi.edu/in-notes/ien/ien74.txt |date=21 December 2008 }}. Cambridge, Massachusetts: Bolt Beranek and Newman, Inc., 21 September 1978.

==References==
{{Reflist}}

==External links==
*[http://www.issn.org ISSN International Centre]

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