Abstract: An alarm lock particularly suitable for use with a bicycle or similar article to be secured, comprising a casing having an integral clamping device and containing an alarm siren which can be actuated either by an internal motion sensitive device, or by breaking or disconnecting a security loop which is connected around the article. Both of the alarm devices are connected to an automatically resettable detector circuit which includes a timer for resetting after a predetermined period. A battery for the circuit is contained in a compartment which is closed by abutment of the alarm lock against the body of the article, when it is attached by the integral clamping device.