Other meanings of International Mobile Equipment Identity
Mobile communications
The International Mobile Equipment Identity (IMEI) is a unique identifier for mobile phones and other cellular devices. Cellular networks use it to distinguish equipment from the subscriber identity and telephone number associated with that equipment, supporting device registration, inventory, diagnostics, and the blocking of reported stolen devices.
An IMEI identifies cellular equipment rather than a person, subscription, or telephone number. Its technical format is specified by the 3rd Generation Partnership Project (3GPP), whose numbering rules are used across GSM, UMTS, LTE, and 5G networks. A conventional IMEI contains 15 decimal digits: an eight-digit Type Allocation Code (TAC), a six-digit device serial number, and a final check digit.
The TAC indicates the approved model or equipment allocation, while the serial portion distinguishes units within that allocation. The check digit is calculated with the Luhn algorithm and helps detect transcription errors; it does not authenticate the device or prevent alteration. A related format, the IMEI-SV, contains 16 digits because it includes a software-version number instead of the ordinary check-digit arrangement.
Manufacturers obtain device-identity allocations through the GSMA system and assign compliant identifiers during production. The GSMA maintains industry services that support device-model information, identity management, and operator checks.1 The identifier is stored in a device's cellular equipment and is presented to a network during procedures such as registration or connection management.
An IMEI is separate from an International Mobile Subscriber Identity (IMSI), which identifies a subscription held on a SIM or eSIM. A phone can therefore retain its IMEI while its subscriber, telephone number, or network changes. Devices designed for two active cellular subscriptions commonly have two IMEIs, one for each radio or logical equipment identity. An eSIM changes how a subscription is provisioned; it does not replace the equipment identifier.
Operators can use IMEI-based equipment blacklists to deny network service to devices reported stolen or otherwise barred. In the United States, the Federal Communications Commission advises consumers to record an IMEI and report theft to both the carrier and law enforcement; carrier practices and the effect of a block can vary by country and network.2
Blocking is not the same as recovering a handset. It may stop cellular use on participating networks but cannot prevent use of Wi-Fi, resale of parts, or operation in jurisdictions that do not share the relevant blacklist. An IMEI also is not a cryptographic proof of ownership. Criminals may alter, duplicate, or falsely report identifiers, and a legitimate-looking IMEI does not by itself establish that a second-hand device is clear, authentic, or legally obtained.
The IMEI's most overlooked detail is that its final digit is mainly an error-detection device, not a security feature. The TAC likewise identifies an allocation or model family, so it should not be treated as a complete description of every hardware revision, market variant, or installed software version.
Users can usually find the identifier by entering *#06#, examining device settings, or checking the original packaging; Apple documents several location methods for its products.3 Android devices expose equivalent information through their settings or packaging, although menus differ by manufacturer. Because the IMEI is persistent equipment information that a carrier can associate with network activity and an account, it should be shared only with trusted parties. It should not be confused with a device's serial number, which is a manufacturer-specific identifier and may have a different purpose.
An IMEI identifies cellular equipment; it is not, by itself, proof of ownership, a subscriber identity, or a guarantee that a used device is free of restrictions.
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