Abstract: In a safety mechanism intended for preventing the locking up of persons in bank strong rooms is incorporated a main latch bolt which is movable between an inoperative position and a protruding position in which it abuts against the strong room door and the associated frame and thereby prevents the closing of the door; in its protruding position the main latch bolt is arrested by an auxiliary latch bolt which, like the main latch bolt, is spring-loaded towards the protruding position; each of the latch bolts is associated with an electromagnet which electromagnets cause, when energized, the retraction of the latch bolts to their inoperative position and are incorporated in a common electric circuit comprising an automatic switch in the strong room floor; normally this switch is closed, but is automatically opened when a person steps on the floor of the strong room, preventing thereby the energization of the two electromagnets and consequently the retraction of the latch bolts.