FIELD: guard systems; signalling systems. SUBSTANCE: when trying open lock by master-key and after the master-key is put into lock hole, somebody wants to turn cylinder 6. But as cylinder 6 is tied with case 4 by pins, the cylinder rotates together with the case for angle α till achieving rest of movable protrusion 12 with motionless protrusion 3; in this case resistance of spring element 13 is overcome. The fact of shift of protrusion 12 has to be the primary signal of feeble attempt of stranger into the room under guard. After the master-key is pulled out of lock hole both movable units (case 4 and cylinder 6) return to initial position. EFFECT: improved reliability. 2 cl, 3 dwg
