GB252771A - Improvements in electric burglar alarms - Google Patents

Abstract

252,771. Eisler, H., Tibbles, H. J. and Rely-a-Bell Burglar & Fire Alarm Co., Ltd. March 2, 1925. Burglar alarms.-A closed-circuit burglar alarm of the kind giving both an audible and visible signal and wherein the normally closed circuit 1 includes switches adapted to be opened and closed by the bolt of a control lock and by the opening and closing of a door respectively, is provided with one or more vacuum tubes 20 in the secondary circuit of an induction coil 19, the primary of such coil being arranged in the alarm circuit which is controlled by the tongue 13 of a relay coil 6 included in the circuit 1. The tubes, which are of Geissler type, are arranged in parallel when two or more are employed. The closed circuit 1 includes a battery 2, a coil 5 on the alarm bell, a relay coil 6 and switch 7, the latter being controlled bv the bolt 8 of a control lock. When the switch 7 is closed by the bolt 8, as shown in the Figure, the tongue 13 is held out of contact with the contacts 14, 15 and the armature 16 is held out of contact with the member 17. The bell circuit 23 includes a battery 24, and a switch 25, which opens automatically when the control lock is unlocked, and is closed when the bolt 8 is locked. The circuit 23 is also controlled by a circuit 26, bridging the contacts of a switch 25, and includes a switch 27 which is closed by the closing of the final exit door so that the bell alarm is actuated if the control lock is not locked. A lifting magnet 28 for the tongue 13 is operated by a push switch 30 arranged in a circuit 29 having a switch 25 controlled by the bolt 8. A circuit 9 is arranged as a shunt to the closed circuit at a switch 4, the members of which are brought into contact when the final exit door is closed. The circuit 9 includes a switch 10 adapted to be operated by hand to close the circuit when the door is open, and is opened by the engagement of the stem 12 with the door when the latter is closed, such an arrangement enabling the circuit to be kept closed during the exit of the person closing the premises. An electric bell 19<a> of the continuously or intermittently ringing type may be arranged in parallel with the induction coil 19. The relay tongue circuit includes a battery &c. 21 and a switch 22 controlled by the bolt 8. Switches 4 are adapted to be opened by unauthorized persons. Specifications 167,361 and 186,787 are referred to.