Abstract: Alarm system for multi-compartment, postal mailbox arrays incorporating a plurality of individual mail compartments contained behind a primary access door. The system comprises an alarm secured adjacent the mailbox array and coupled thereto by switches coupled to each access door and to the postal lock for that door. The postal lock is modified with an aperture which exposes the internal operation thereof for a switch mounted thereon. In this manner authorized actuation of the lock disengages the alarm system to prevent it from sounding when the access door is opened. Forced opening of the access door without first disengaging the system through the postal lock will otherwise set off the alarm. In this manner a number of access door switches may be coupled to a single alarm box which itself may be constructed for preventing unauthorized deactivation by the utilization of similar switch sensors disposed therein.