GB597041A - Improvements in or relating to electric theft alarms - Google Patents

Abstract

597,041. Hand actuating devices for switches. BROWN, J. C., and BROWN, H. B. Feb. 27, 1945, No. 4892. [Class 38(v)] [Also in Group XXXVIII] In an electric theft-alarm system for vehicles a key-operated ignition switch is provided of the kind set forth in Specification 522,423 but of different construction. The switch has main contacts 13, Figs. 2 and 8, for preparing an alarm circuit, which is then completed upon movement of such parts of the vehicle or the like as may be desired, and auxiliary contacts 14 operated by a key with false wards to close the alarm circuit. Each main contact 13 is arranged adjacent an auxiliary contact 14 each being prevented from rotation by a projection 35, 37 engaging in a slot 36 in the switch casing 10, and each pair of contacts 13, 14 being separated by a spacer assembly consisting of discs 16, interlocking with each other and with the adjacent auxiliary contact, retained within an annulus 15. When a correct key 38 is inserted its wards retract spring-loaded slides 20, 20 mounted within a disc 18 of each main contact so that they are now clear of lugs 44 on a locking bar 39. When the key 38 is fully inserted its end pushes back a spring-loaded plate 43 which moves the locking bar 39 to the left, disengaging the lugs 44 from a notch 45 in each master contact 13 and engaging them instead in a semi-circular slot 19a which permits the key 38 to rotate master contact discs 18 through 180 degrees, in which position a contact strip 22 on each disc 18 bridges terminals 17, 17 to prepare the alarm circuit. When the key is now withdrawn the locking bar 39 returns to the right where each lug 44 engages a second, diametrically opposed, notch 45 in the contact discs 18, and the slides 20 move radially outwards to lock the bar 39 in this position. The switch can now be unlocked only by a key having the correct wards. Insertion of a false key will result in one or more of its wards engaging either an auxiliarly contact 14 or one or more of its interlocked spacer discs 16, Rotation of such a key in either direction will therefore turn an auxiliary contact disc and result in the terminals 27, 27 being bridged to close the alarm circuit, which is self-locking so that the alarm remains operated even if the key is withdrawn.