Abstract: An apparatus for monitoring the closed position of a locking gas cap (10) with a magnet (32) disposed at or in the locking gas cap and a solenoid (42) disposed at the tank connection pipe (12), the locking gas cap (10) having a torque limiter (36), and the magnet (32) being coupled with the torque limiter in such a manner, that it reaches a position, in which the solenoid (42) is triggered, only when the limiting torque is reached.