What is a serial number on a product?

A serial number is a code given to one individual unit of a product. Every phone, washing machine or e-bike battery of the same model shares a model number and a GTIN, but each one has its own serial number. That makes it possible to know exactly which unit someone owns, returns, repairs or scans.

How serial numbers work in the GS1 system

The GS1 General Specifications define Application Identifier (21) for the serial number. The rules are short:

• Lifetime: "A serial number is assigned to an entity for its lifetime."
• Unique with the GTIN: "When combined with a GTIN, a serial number uniquely identifies an individual item." Two different products can both have serial 0001, but the same GTIN must never repeat a serial. The brand owner and manufacturer are responsible for that.
• Format: up to 20 alphanumeric characters, from the GS1 character set.

The combination of GTIN and serial number is called an SGTIN, or serialised GTIN. The GS1 EPC Tag Data Standard uses it "to assign a unique identity to an instance of a trade item", for example on RFID tags.

In a barcode the two are written as element strings, such as (01)09506000134352(21)A1B2C3 in a GS1 DataMatrix. In a QR code built on GS1 Digital Link they become a web address:

https://example.com/01/09506000134352/21/A1B2C3

A checkout scanner can read the GTIN from that address, and a phone opens a page for that exact unit. Because the serial changes on every unit, these codes are printed with variable data on the line or on labels, rather than preprinted on packaging.

What serial numbers are used for

• Warranty and registration: the serial number proves which unit was bought and when its warranty started, and it stays with the unit if it is resold.
• Recalls and safety notices: when a fault affects a known range of units, serial numbers let you contact only those owners. The General Product Safety Regulation, Article 9(5), accepts a type, batch or serial number as the element that identifies a product.
• Repair and service history: technicians can log parts and repairs against the unit, which supports refurbishment and resale.
• Counterfeit protection: a unique, hard-to-guess serial can be checked against the brand's records. EU medicines go further: Delegated Regulation (EU) 2016/161 requires a serial number of up to 20 characters, generated by a randomization algorithm, encoded in a Data Matrix on each pack.
• Supply chain traceability: serialised items can be followed event by event through logistics systems.

Serial numbers and the Digital Product Passport

ESPR Article 9(2)(d) lets each product group's delegated act set the passport at model, batch or item level. Recital 33 describes an item as "a single unit of a model". At item level, every unit needs its own unique product identifier, and the usual way to build one is a GTIN plus a serial number.

Batteries are already at item level. Article 77 of the Battery Regulation requires a battery passport from 18 February 2027 for each LMT battery, each industrial battery above 2 kWh and each electric vehicle battery. It holds information on the model and on the individual battery, and is reached through a QR code that links to a unique identifier the economic operator attributes to that battery (Article 77(3)).

How to generate serial numbers

1. Pick a format of 20 characters or fewer if it will go into a GS1 barcode. Avoid characters that are easy to confuse, such as O and 0.
2. Choose sequential or random. Sequential serials are easy to sort and to group into ranges. Random serials are harder to guess, which helps against counterfeits.
3. Add structure if useful, such as a prefix, the production year or a batch code, but keep the serial unique on its own for each GTIN.
4. Never reuse a serial for the same GTIN, even across factories or years.
5. Store each serial with its context: GTIN, batch, production date and site.

The free serial number generator creates up to 10,000 serial numbers at once, and can add a GTIN to turn each one into a GS1 Digital Link for a QR code per item.