Device and method for detection of an external energy supply in particular of an automobile

The device for detecting an unauthorized start is installed in a vehicle that has an electrical on-board power supply system (14) which is supplied by a vehicle battery (10) with an on-board power supply voltage of approximately 12.5 V. A negative terminal (11) of the battery (10) is connected to a vehicle ground (15). Between a positive terminal (12) of the battery (10) and the on-board power supply system (14), a monitoring unit (13) is arranged. In the monitoring unit (13), a conventional voltage sensor (20) for detecting the on-board power supply voltage, likewise a conventional current sensor (21) for detecting the current flowing from the battery, as well as a conventional temperature sensor (22) for detecting the operating temperature of the battery (10) are provided. The main measured variable is the on-board power supply voltage; the battery current and the battery temperature represent auxiliary measured variables in the monitoring algorithm. Furthermore, the monitoring unit (13) contains a microcontroller (23) which can detect a change in the on-board power supply load via a CAN bus (25). As indicated by the dashed line (26), the on-board power supply load can also be detected directly via a controllable switch (24).