Device and method for preventing a parked car from being stolen and monitoring a parked car

The method involves monitoring the vehicle parked parking space by the sensors, where the sensor signal is evaluated by an evaluation unit upon modification and a warning signal is given upon existence of a pre-determined signal change. The terrestrial magnetic field over the parking space is recorded by magnetic field sensors according to parking of a vehicle in a parking space and is stored in the form of vehicle-specific magnetic field reference data. An independent claim is also included for a device for theft-deterrent system or monitoring a parked vehicle.