What is a serial number?
A serial number is a unique identification code that a manufacturer assigns to one individual unit of a product, device or component, so that this single unit can be identified, traced and managed throughout its entire life cycle. Two PLCs with the same order number are of exactly the same type, but each has its own serial number. That lets you link warranty, firmware version, calibration and maintenance history to exactly that one device. In industrial environments, the serial number is the bridge between the physical device in the cabinet and the digital records in asset management, the CMMS and the ERP system.
Serial numbers make it possible to distinguish between seemingly identical devices.
🧠 What is the difference between a serial number, a type number and a batch number?
A nameplate usually carries several numbers side by side. They are often confused in practice, even though each has a different purpose:
| Number | Applies to | Assigned by | Purpose |
|---|---|---|---|
| Serial number | One individual unit | Manufacturer | Identification and traceability per unit |
| Type number / order number | All units of one version | Manufacturer | Specification, compatibility and ordering |
| Batch number / lot number | A group of units from one production run | Manufacturer | Recalls and quality investigations per production lot |
| GTIN | A trade item (product type) | Manufacturer via GS1 | Globally unique product code across the supply chain |
| Asset or tag number | A function or position in the plant | Plant owner | Place in the process, independent of which unit is installed |
The last distinction matters in OT. The tag number (for example a pump or transmitter at a fixed position) stays the same when you replace a faulty device, whereas the serial number changes. Good records therefore capture which serial number sat at which position at which time.
🎯 What is a serial number used for?
| Use case | Description |
|---|---|
| Warranty and service | Proving that the product is within warranty and retrieving the correct support history |
| Traceability | Determining when, where and in which production revision a component was made |
| Configuration management | Linking firmware and software versions to specific hardware |
| Asset management | Tracking the location, status, calibration and maintenance history of a device |
| OT-specific | Uniquely identifying PLCs, sensors, HMIs or IO cards |
| Authenticity check | Verifying with the manufacturer whether a unit is genuine, useful when buying through unofficial channels |
🔧 What does a serial number look like and where is it shown?
A serial number is usually a string of digits and/or letters, such as SN-2025-004183. There
is no general standard for its structure: each manufacturer chooses its own format. It often encodes
meaning such as the year and week of production, the factory or the production line. A serial number is
unique within one manufacturer’s numbering (and often within one product type), but not globally. Global
uniqueness only arises in combination with the manufacturer or the product code.
That is why identification standards combine the serial number with a product type:
- GS1 - Application Identifier (21) encodes a serial number of up to 20 characters. Together with the GTIN it forms a serialised GTIN (SGTIN), which is unique to one unit. This is printed as a DataMatrix, QR code or GS1-128 symbol, or stored in an RFID tag.
- UDI - medical devices receive a Unique Device Identifier whose production part contains a serial number or lot number.
- IEC 61406-1:2022 (Identification Link) - specifies how a globally unique identifier in URL form is applied to a product, through a 2D code or NFC tag. At Siemens, such a link contains the article number and serial number, among other things; the QR code is recognisable by a frame with a small triangle at the bottom right. Scanning it leads straight to the product information for that specific unit.
Physically, the serial number is printed on the nameplate or a label, often with a barcode. In modular systems such as PLC racks, every module has its own serial number. Note that modules mounted inside a cabinet are sometimes only readable after removal, which is why reading serial numbers digitally is so valuable in OT environments.
🏭 How do you read serial numbers digitally in OT networks?
Modern field devices and controllers expose their serial number over the network. This allows asset discovery tools and engineering software to build an up-to-date asset inventory without anyone opening the cabinet:
| Protocol / model | Where the serial number lives | Characteristics |
|---|---|---|
| PROFINET / PROFIBUS | I&M0 record (Identification & Maintenance) | Serial number 16 characters, order number 20 characters; I&M0 is read-only, I&M1–3 can be written by the user |
| IP (CIP) | Identity Object, attribute 6 | 32-bit integer; readable with ListIdentity |
| OPC UA |
SerialNumber property in the nameplate model of the Devices (DI) companion
specification
|
Optional string, intended for traceability and warranty |
| SNMP | entPhysicalSerialNum in the ENTITY-MIB |
Common on switches, routers and IT hardware |
| Asset Administration Shell | Digital Nameplate submodel (IDTA 02006) | Digital nameplate of the unit, can be linked to an IEC 61406 code |
For illustration, some typical combinations of order code and serial number. The serial numbers are fictitious; the first part is always the type or order code that is identical for all units:
| Component | Order code + (fictitious) serial number | Use of the serial number |
|---|---|---|
| Siemens PLC (CPU 314C-2 DP) | 6ES7 314-6CG03-0AB0 + S/N X1234A7 |
Linking to project configuration and firmware level |
| ABB variable frequency drive (ACS580) | ACS580-01-07A6-4 + SN FJ88322103 |
Firmware management and maintenance history |
| Schneider Electric HMI (Magelis) | HMIGTO5310 + SN GT1045693B |
Field replacement or support ticket |
| Industrial laptop | S/N A1B2C3D4E5 |
IT asset management within the OT environment |
🔐 Why do serial numbers matter for security and compliance?
A serial number is not a security control in itself, but it underpins many controls:
- Legal identification duty - the Cyber Resilience Act (Article 13(15)) requires products with digital elements to bear a type, batch or serial number or another element allowing their identification, or to provide this on the packaging or in an accompanying document. CRA reporting obligations apply from 11 September 2026 and full application from 11 December 2027. The Machinery Directive also lists the serial number (where applicable) as a mandatory marking on machinery in Annex I, section 1.7.3; the Machinery Regulation replaces that directive from 20 January 2027.
- Asset inventory for NIS2 - under NIS2 and the Dutch Cybersecurity Act (Cyberbeveiligingswet), organisations must know their systems. An inventory with serial numbers shows which units are affected by a vulnerability advisory and which are not yet patched (vulnerability management and patch management).
- Supply chain risk and counterfeits - counterfeit or grey-market hardware is a real supply chain risk. A serial number the manufacturer does not recognise, or one that appears twice in your plant, is a red flag.
- Not a secret - a serial number is publicly readable and often retrievable over the network. Never use it as a password or as the sole means of authentication; default passwords derived from the serial number should be replaced at commissioning.
🛠️ How do you set up serial number management in practice?
An example: a Dutch water board replaces a faulty IO card in a pumping station. Without serial number records, it is impossible to establish afterwards which firmware the new card had and whether it is covered by an advisory published later. A simple approach prevents this:
- Record serial numbers on receipt - scan the barcode or 2D code on arrival and link the unit to the purchase order.
- Link serial number to tag number - at installation, record the position the unit goes into, with date and firmware version.
- Read digitally on a regular basis - compare what the network and the engineering tool report (for example PROFINET I&M0) with your records; differences point to undocumented replacements.
- Record every swap - on replacement, the tag number stays, while the old serial number moves to the history in the CMMS together with the failure reason (part of change management).
- Use it for incidents and advisories - when a vendor publishes a vulnerability advisory, check immediately which units and firmware versions in your plant are affected.
❓ Frequently asked questions
Where can I find the serial number of a PLC?
The serial number of a PLC is printed on the nameplate or a label on the module, often also as a barcode. On modern PLCs you can also read the serial number through the engineering software or over the network, for example via the PROFINET I&M0 record or the EtherNet/IP Identity Object. Every module in a rack has its own serial number.
Is a serial number globally unique?
A serial number is usually only unique within the numbering of one manufacturer or one product type. Global uniqueness arises only when the serial number is combined with a manufacturer or product code, as in a GS1 SGTIN (GTIN plus serial number) or an IEC 61406 Identification Link.
What is the difference between a serial number and a batch number?
A serial number identifies exactly one unit, whereas a batch number refers to a whole group of units from the same production run. A recall based on a batch number affects every unit in that lot; with a serial number you can pinpoint individual units.
Is a serial number mandatory under the Cyber Resilience Act?
The Cyber Resilience Act requires manufacturers to give products with digital elements a type, batch or serial number or another identifying element. A serial number specifically is therefore not mandatory, but the product must be identifiable. If that is not possible on the product itself, the information may be provided on the packaging or in an accompanying document.
Can a serial number be reused?
A serial number is not reused: after a device is replaced or scrapped, its serial number stays linked to that one unit and its history. Reuse would make warranty claims, recalls and traceability unreliable. With an exchange repair you often get a different unit back with a different serial number, so record that swap in your records.
Can a serial number be forged?
A serial number on a label or nameplate is easy to copy, so on its own it does not prove that a device is genuine. Manufacturers often offer a check through their website or support, and duplicate serial numbers in your own inventory are a clear warning sign. Stronger authenticity guarantees require cryptographic device identities, such as an IEEE 802.1AR IDevID certificate that the manufacturer installs in the device during production and that usually includes the serial number.
📌 In summary
A serial number is a unique code by which you can recognise, track and manage a specific device or component. In industrial environments, this is essential for maintenance, firmware updates, compliance and asset management: combine the serial number with the tag number, firmware version and history, read it digitally where possible via PROFINET, EtherNet/IP or OPC UA, and never use it as a secret.