Anti-theft system employing coincidence switch with easily-changed combination

Claim 1

An anti-theft system comprising an electric circuit which includes at least one switch to be operated by a closure member, a relay having a coil to be energized by operation of said switch and having contact means with an alarm whereby operation of said relay will cause operation of said alarm, and a single manually operable coincidence switch having selectable positions of coincidence in circuit between said one switch and said relay and having a particular position of coincidence in which it renders the anti-theft system inoperative, said coincidence switch including two manually rotatable dials each having corresponding characters for setting against datum points, one of said dials being positioned externally of said coincidence switch and intended for access externally of the enclosure to be protected, a contact pin connected to one of said dials for movement therewith, a circular contact plate connected to the other of said dials for rotation therewith and being in contact with said contact pin, said plate having a small portion of insulating material whereby when said dials are set to correspond said contact pin bears against said portion of insulating material so that said coincidence switch is in an ''off'' condition, whereas when the setting of said two dials do not correspond said contact pin makes contact with said contact plate to complete a circuit through the switch and render the system operative, said coincidence switch comprising a tubular housing, a front cover positioned on said housing, said one of said dials being rotatably positioned in said front cover, means for manually rotating said one dial whereby any character of said dial can be set against said datum point, said plate being a metal disc having said small portion of insulating material therein and being drivingly connected with said one of said dials, said metal disc being connected in the electrical circuit of the anti-theft system by means of a terminal device associated therewith, a disc of insulating material carrying said contact pin which is metal and is connected electrically by means of a further terminal device in the circuit of the anti-theft system, a spring loaded plate urging said contact pin into rubbing contact with said metal disc, a stem on said disc carrying said contact pin, said stem being connected with the other of said dials being positioned at the opposite end of said housing to said one dial, and means for locating said other dial in any selected position of adjustment.