Patent ID: 6857671

Claim:
A locking device for a door comprising: a backing plate which is connectable to a door or a door frame; an electromagnet; a housing for the electromagnet, the housing being movable away from the backing plate between a first position and a second position, and towards the backing plate between the second position and the first position; biasing means for biasing the housing into the first position; an armature plate which is displaceable relative to the housing between a closed condition in which it engages the housing and an open condition in which it is spaced from the housing; and mechanical locking means in the form of at least one locking arm which is movable between an operative position in which it engages the armature plate and the backing plate to capture the armature plate in the closed condition and an inoperative position in which it allows the armature plate to disengage the housing, the at least one locking arm including a formation which is engageable with a corresponding formation on the backing plate so that as the housing is displaced from the first position to the second position the locking arm is displaced from the inoperative position to the operative position.