Abstract: An alarm system for detecting attempted theft of an article includes means incorporated in the article itself and arranged to transmit and to continuing transmitting an alarm signal when the article is removed from its original location. An example of the alarm system provides an audible alarm, or transmitted alarm, and is arranged to be operated when a thief removes or attempts to remove a car radio, cassette player, compact disc player or the like from a car. Unauthorized removal of the unit from a car is detected by the consequent breaking of an electrical circuit which may be the power supply connections to the radio from the car electrical system or may be the connections to the loudspeakers or the radio aerial.