Abstract: Alarm type lock assembly comprising a cylinder having a core rotatably disposed therein, a key slot extending through the core, a plurality of bores extending into the key slot, tumblers disposed in the bores and spring biased to a first position in which the tumblers prevent rotative movement of the core, a key adapted to enter the slot and operative to move the tumblers to a second position to permit rotative movement of the core, and contact points aligned with the tumblers and in circuit with an alarm means, the tumblers being movable to a third position in which the tumblers engage the contact points to energize the alarm means and prevent opening operation of the lock.