Abstract: The trigger mechanism is an electronic switch comprised of an LED and a photosensitive transistor. The active surfaces of the LED and photosensitive transistor are normally aligned, the LED being suspended by a wire from a support above the transistor. Vibration or movement above a given magnitude results in misalignment of the active surfaces which causes the transistor to generate a trigger signal. The sensitivity of the electronic switch is adjustable by varying the spacing between the active surfaces. A delay circuit is interposed between the electronic switch and the remainder of the alarm circuitry such that generation of the alarm signal is prevented for a preset time interval after the arming of the device in order to permit the electronic switch to achieve mechanical equilibrium.