What Is an IMEI Number?

Last updated: October 2025 · 5 min read

IMEI stands for International Mobile Equipment Identity. It is a 15-digit number that uniquely identifies a mobile device — your phone itself, not your SIM card or your account. Every phone that connects to a mobile network is assigned at least one IMEI during manufacturing, and that number stays with the hardware for its lifetime.

What the 15 Digits Mean

An IMEI is not a random number. Its digits follow a defined structure specified by the GSMA (the global mobile industry standards body):

The TAC (Type Allocation Code)

The first 8 digits form the TAC. This code is assigned to a specific device model by the GSMA — for example, all iPhone 13 units from the same manufacturing batch share the same TAC. The TAC allows mobile networks and databases to identify a device type by its IMEI alone, without needing to communicate with the phone. See our TAC code guide for more detail.

The Serial Number

Digits 9 through 14 are a serial sequence allocated by the manufacturer within that TAC. Together with the TAC, these six digits make each IMEI unique across every device with that model designation.

The Luhn Check Digit

The final digit is calculated from the preceding 14 using the Luhn algorithm — a simple checksum that helps detect typographical errors. If you enter an IMEI and the last digit doesn't match what the formula predicts, the number was either entered incorrectly or is not a genuine IMEI. Passing the Luhn check means the number is correctly formatted — it does not mean the phone exists or is legitimate in any other sense.

What an IMEI Can Tell You

How Carriers Use the IMEI

When a phone connects to a mobile network, the network checks the IMEI against an Equipment Identity Register (EIR). This database tracks which IMEIs are allowed ("white list"), barred ("black list"), or flagged ("grey list"). Carriers in the same country often share this database through industry bodies such as the CTIA in the US or the GSMA globally.

A blacklisted IMEI is refused by the network. The phone may still connect to Wi-Fi, but it cannot make calls, send texts, or use mobile data — on any carrier that queries the same database.

IMEI vs SIM Card vs IMSI

It helps to distinguish these three identifiers:

• IMEI — identifies the device (the hardware). It does not change when you swap SIM cards or carriers.
• SIM card (ICCID) — identifies the SIM card itself, not the phone. Swapping the SIM does not change the IMEI.
• IMSI — the International Mobile Subscriber Identity, stored on the SIM, identifies your account with the carrier. Also not tied to the hardware.

Because these are separate, a SIM swap does not change an IMEI. A phone reported stolen and blacklisted by its IMEI stays blacklisted regardless of which SIM is in it.

Dual-SIM Phones and Multiple IMEIs

A phone with two physical SIM slots, or one SIM slot plus eSIM, is assigned two IMEI numbers — one per slot. You can see both by dialling *#06# or checking Settings. For a thorough used-phone assessment, check both IMEI numbers, since a network block can apply to either one independently.

Why Your IMEI Is Sensitive

Your IMEI is not a secret in the way a password is, but it is not something to share publicly either. Someone with your IMEI could, in theory, report it to a carrier as stolen (though this requires them to be the account holder), or use it to clone a device for fraudulent purposes. When buying or selling a phone, share the IMEI only with verified parties for the specific purpose of verification.