IMEI (International Mobile Equipment Identity) is a unique number which is used to identify WCDMA, GSM, iDEN mobile phones and also some satellite phones. It is a 15 or 17 digit number which can be found behind the battery. This number is used by networks to block stolen phones from accessing the network and to identify the valid phones. This number can be displayed on the screen by entering *#06# on the keypad. The IMEI code may be printed inside the battery compartment. When a phone set is lost or stolen, the owner can call the CEIR (Central Equipment Identity Register) and blacklist the device according to its IMEI number.