The RFID is a passive transponder usually embedded in the key but can be standalone as with M3W. The car immobiliser transceiver in the steering column sends out pulses of a very weak RF signal at 13.56 MHz which the transponder in the key bounces back modified with its unique code. The transceiver gates out any incorrect code but allows correct to disable immobiliser. Being a very weak therefore range sensitive signal added to the anomalies of RF transmission there are many factors contributing to it not functioning correctly.
