A lock operable by a key between a locked condition and an open condition, the lock having a fastener for releasably securing the lock to an object, the fastener being movable between a retracted position wherein the lock is in the open condition and an extended position, a spring for biasing the fastener to the retracted position and an enclosure having an opening adapted to allow the insertion and removal of the key from the lock when the lock is in the locked condition and to prevent the removal of the key from the lock when the lock is in an unlocked condition.