The structure of an IMEI
Every IMEI has three parts. Take 35 391808 123456 5 as an example:
- TAC, the Type Allocation Code: the first 8 digits (35391808). It is assigned by the GSMA and identifies the exact model and variant. The first two digits are the Reporting Body Identifier.
- Serial number: the next 6 digits (123456), unique for each unit of that model.
- Check digit: the last digit (5), calculated from the other 14 with the Luhn algorithm. It catches typos.
IMEI, IMEISV and serial number
IMEISV is a 16-digit variant: the same TAC and serial followed by a two-digit software version instead of the check digit. Some diagnostic screens show it.
The serial number is the manufacturer's own identifier, used for warranty and service. Apple, for example, keys coverage to the serial. It is a different number from the IMEI, and both are listed in Settings.
Older CDMA phones used a MEID instead, a 14-character hexadecimal number. Modern phones that support both network types have an IMEI.
Why dual-SIM phones have two IMEIs
Each cellular modem slot gets its own IMEI, so a dual-SIM or SIM-plus-eSIM phone shows two. Either one identifies the device; checks like Activation Lock give the same answer for both.
What an IMEI is used for
- Networks use it to identify the device and to block phones reported stolen.
- Manufacturers and repair shops use it to look up model, warranty and service history.
- Buyers use it to verify a used phone before paying, which is what IMEI.si is for.
Frequently asked questions
Is it safe to share my IMEI?
Sharing it with a buyer or a checking service is normal. An IMEI identifies hardware, not you. Avoid posting it publicly next to your name and phone number.
Can an IMEI be changed?
It is stored in protected hardware. Altering it is illegal in many countries, including the UK and much of the EU.
Last updated 12 October 2026