Abstract: A sensor system for security purposes comprises a piezo-electric device (F) attached to a member (E) in the line of stress flux such that unauthorised movement of the member will result in deflection of the piezo-electric device and generation of an electrical output. The electrical output is passed to an electronic control circuit (H) which includes filter means (LPF) for separation of signals due to high-frequency events and is arranged to transmit a signal to an alarm.

Abstract: A sensor system is provided for use in detecting movement of an item, e.g. a picture 16, suspended from a wall or other substantially vertical structure, or for detecting movement of an item displayed or stored on a horizontal or inclined surface, the sensor system including a piezoceramic element (22) which is mounted on a metallic disc (23) which, in use, is located between the item (16) and the structure or surface, and means for detecting the generation of an output by the piezoceramic element (22) as a result of deflection of the disc (23) in either of two opposite directions as a result of movement of the item (16).

Abstract: A sensor system is provided for use in detecting movement of an item, e.g. a picture 16, suspended from a wall or other substantially vertical structure, or for detecting movement of an item displayed or stored on a horizontal or inclined surface, the sensor system including a piezoceramic element (22) which is mounted on a metallic disc (23) which, in use, is located between the item (16) and the structure or surface, and means for detecting the generation of an output by the piezoceramic element (22) as a result of deflection of the disc (23) in either of two opposite directions as a result of movement of the item (16).