Abstract: An anti-theft alarm system for movable objects, particularly motorcycles, and actuated by mechanical disturbance, e.g., by using tools on a vehicle, moving it off its stand, or operating it. The primary disturbance sensors are steel balls or the like in small compartments inside which they are free to roll. Impacts of one or more balls against compartment walls generate pulses of high-frequency sound and vibration, which are in turn sensed by an adjacent high-frequency microphone or vibration pickup. The output of this transducer is then amplified and suitably processed to energize a horn or other alarm device.