Radio-frequency fingerprinting

A process that identifies a cellular phone by the unique "fingerprint" that characterizes its signal transmission. RF fingerprinting is one process used to prevent cloning fraud, because a cloned phone will not have the same fingerprint as the legal phone with the same electronic identification numbers. (Cingular)

Location software calculates the location of tracked devices using techniques such as RF fingerprinting, which uses assesses RF characteristics such as reflection, attenuation, and multi-path, along with the signal strength readings of wireless devices calibrated RF environments. (Wikipedia)