Detection Coil

A detection coil is mounted at the ignition lock as an integral part of the key position trim ring. The wires to and from the detection coil are connected to the immobilizer. When the ignition is turned ON, the immobilizer energizes the detection coil and the coil is coupled inductively to the transponder in the ignition key. The immobilizer sends a modulated signal to the detection coil. The signal is changed by interaction with the internal transponder in the ignition key. The immobilizer reads the signal from the detection coil and determines whether the key is authorized.