Electronic immobiliser.

Better protection against theft: the electronic immobiliser prevents unauthorized entry into your BMW and prevents it being started, unless your correct individual key code is properly provided.

The electronic immobiliser secures your car using a chip with an electronic code integrated in the car key. This code consists of a permanent personal code and a second code changed by the immobiliser each time you start the engine.
Whenever the ignition is switched on, the immobiliser first reads the personal code and then asks for the changing code. If both answers are correct, the immobiliser will send another coded signal to the Digital Motor Electronics (DME) to unlock the engine. Without which the engine cannot be started - not even by short-circuiting it.
This data is transmitted wirelessly via an aerial in the steering wheel lock and the key with integrated remote control. The key is equipped with a maintenance-free battery which recharges automatically while driving. And should you ever lose your key, you can have it deactivated by your authorised BMW dealer and receive a replacement key without delay.