Passive coil
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Land Rover Discovery, 2003 Land Rover Discovery, 2002 Land Rover Discovery, 2001 Land Rover Discovery, and 2000 Land Rover Discovery. However, it is still accessible from the selected car via links, so may be relevant.
The passive coil is located around the ignition key barrel. When the BCU detects that the ignition key has been turned to the crank position, the vehicle's immobilization system is activated and a signal is sent to the passive coil at a frequency of 125 kHz. The magnetic field generated in the coil is induced in the remote transmitter to trigger a re-mobilization signal.