In a vehicle alarm system, as one feature circuitry is provided which can be attached to detect an input from a door pin input switch, and which can detect the opening and closing of the door if the door pin input switch is either a positively triggered pin switch or a negatively triggered pin switch. Furthermore, a specific structure of a piezoelectric disk sensor and detecting circuitry associated therewith is provided. The piezoelectric disk sensor has a weight mounted off a central axis at a distance of approximately a radius of the piezoelectric disk from a rigid mounting area. The associated circuitry evaluates all information from a shock sensing signal detected by the piezoelectric disk sensor.