Abstract: An anti-tamper device for detecting relative movement between a part (25) having a stud (12; 83) clamped to a mounting (24) by a nut (13; 55). The nut (13; 55) holds a sensor (7, 8, 9, 10; 41, 52, 54) in a conductive condition but, when the part (25) is removed from the mounting (24), the sensor (7, 8, 9, 10; 41, 52, 54) becomes non-conductive. A circuit is provided to provide and detect the change of state of the sensor to provide an alarm. The device may be used to detect the removal of a keypad from a mounting.