Abstract: An apparatus for triggering a warning device, in particular in a vehicle with an on-board controller to influence braking pressure and/or engine torque and/or steering as a function of the movement behavior of the vehicle wheels and/or of the vehicle, is described. In the event of a fault in the controller, ground is applied to the warning device by a control unit of the controller and the fault is thereby indicated. At least one comparator is provided, to which on the one hand a comparison voltage and on the other hand a further voltage can be applied, such that the comparator becomes conductive and applies to the warning device the ground applied to it, if the further voltage is less than a first comparison voltage and/or if the further voltage is greater than a second comparison voltage.