Abstract: Vehicle alarm apparatus including a control circuit for energizing the horn of the vehicle upon the unauthorized tampering with selected parts of the vehicle. A reed switch is mounted adjacent the gas tank fill pipe so as to be operated by a magnet mounted in movable relation thereto, as, for example, on the closure door for the fill pipe, and a control circuit is provided which has a plurality of connecting points, each of which can be connected to a variety of existing circuits of selected electrical components of the vehicle including the reed switch circuit. The control circuit is capable of energizing the horn of the vehicle in response to a predetermined change of condition in such circuits, even where the predetermined changes of the circuit conditions for the various circuits are dissimilar.