Abstract: A security system for a vehicle comprises a sensor assembly which can be releasably mounted to a vehicle or to an item contained therein. The sensor assembly includes a sensing device that is actuated upon sensing a predetermined change in inertia relative to the assembly. The sensing device actuates a transmitter within the sensor assembly to transmit a signal upon detection of the predetermined level of inertial change. The security system further includes a receiver/transmitter unit mounted near the sensor assembly for receiving the transmitted signal and then transmitting an amplified signal to a remote station. The receiver/transmitter unit may be operatively connected to the horn or lights of the vehicle so as to foil a potential thief who presumably initiated the inertial change that activated the alarm. The remote station also includes audible and visual alarms for alerting a vehicle owner of the theft that is potentially in progress at the site of the vehicle.