The International Mobile Equipment Identity or IMEI
It is usually found printed inside the battery compartment of the phone, but can
also be displayed on-screen on most phones by entering *#06# on the dialpad, or
alongside other system information in the settings menu on smartphone operating
systems.
The IMEI number is used by a GSM network to identify valid devices accessing their
network.
The IMEI (15 decimal digits: 14 digits plus a check digit) or IMEISV (16 digits)
includes information on the origin, model, and serial number of the device.