Abstract: An alarm system for locking receptacles having an actuating arm, such as a latch bolt, engaging a fixed portion of the receptacle, the system including a switch having an arm for engageably coacting with the actuating arm in the locked position, with the switch open. Upon removal of the actuating arm, by force or otherwise, the switch arm, which is normally biased to a closed position, is released to activate an alarm circuit which includes a power source and a horn or bell or the like. Retaining means are provided to engage the switch arm to maintan it against its bias to inactivate the alarm system when access to the locking receptacle is desired by an authorized person.