IMEI is an abbreviation for International Mobile Station Equipment. It is a specific and unique number that is used to track down and identify mobile phones and satellite phones that use 3G, IDEN, or another form of the phone network.
The number can be found printed in the battery compartment, displayed on the screen by typing *#06# on the phone keyboard, or found in Android settings with the rest of the phone's details.
Many countries use the IMEI phone number in law to reduce theft and tracking; for example, mobile operators in Singapore implemented a phone blocking and tracing system based on the IMEI; and in the United Kingdom, under the Mobile Telephones Act, changing the IMEI or possessing equipment to do so is an offense.
The IMEI has 15 decimal digits, 14 decimal digits, and a check digit. Those numbers are separated into groups, and each group of numbers tells us something different about the phone. Tac indicates that it is issued by the BABT, FAC – when the phone was manufactured, SNR – unit identifying numbers, CD – GSM phase 2 or higher, and SVN – software version number.
The IMEI number is most commonly used to prevent theft. When your equipment is stolen or misplaced, you can contact your local operator and request that the device be blacklisted, rendering it inoperable on the network; you can only use the mobile phone portions.
However, with the right tools, it is simple to change the IMEI. Australia was the first country to introduce IMEI blacklisting in its GSM network in 2003. In the United Kingdom, the Metropolitan Police Service actively checks IMEI against the National Mobile Property Register for registered phones engaged in crime.
Thuraya satellite and Broadband Global Area Network Iridium employ IMEI on their transceivers as well as SIM cards, just as the GSM network. The iridium 9601 relies on the IMEI number and does not require a SIM card, however, the network is proprietary, and the device is incompatible with terrestrial GSM networks.
Tracking a mobile phone by IMEI could be beneficial if you misplace your device or it is stolen. Your local GSM operator is capable of tracking down the user and acting in accordance with the law. The IMEI is used to identify the device and has no long-term or semi-long-term relationship with the user or subscription.
The SIM card stores the IMSI number, which can be transferred to a headset. When a subscriber is detected, the IMSI number is transmitted between the two devices.