Patent GB-669820-A (GB)
Title: Improvements in electric alarm devices
IPC: G08B19/00
Filed: 1948-03-06
Abstract: 669,820. Burglar and like alarms. WESTAWAY, J. April 6, 1949.. [March 6, 1948; Aug. 12, 1948] Nos. 6982/48 and 21259/48. Class 118 (i). A burglar alarm system of the currentnormally-flowing type comprises an accumulator 1, connected via a float-charger 3 to supply mains 2, a relay coil 4, normally energized to hold contacts 5 closed and contacts 6 and 7 open (as shown), a control switch 18 having a "test" position indicated by the dotted connections and a "protection"position, shown in full, and a selector switch 8 which determines how much of the protection circuit 9, 10, 11 shall be in use. An internal alarm device 15a and an external alarm device 15 are connected to the supply in series with contacts 6 and 7 respectively, so that should any of the detector switches in circuits 9, 10, or 11 be opened the alarms are sounded by relay 4 releasing to allow contacts 6 and 7 to close. The external alarm device 15 also forms a series circuit with relay coil 4 and a 1 amp fuse 16, the current flowing being insufficient to operate the alarm device but tampering with its hammer breaks the circuit, relay contacts 5 open, contacts 6 and 7 close and both alarms become operative. Moreover, if the wires to device 15 are cut the temporary short-circuit blows fuse 16 thereby de-energizing the relay and sounding the internal alarm. When switch 18 is placed in the "test" position (shown dotted) the lamp 21a will light if the protection circuits are complete. The main components may be housed in a common container having a lock and provided with a switch such that tampering therewith will sound the alarm ; the external alarm 15 may be in a casing similarly protected. Preferably the control and selector switches are key operated by the same key. In a modification illustrated in the drawing accompanying the complete Specification (not shown), a system having two selector switches is provided, also a "duplicate" circuit the wires of which are run alongside the main protection circuits such that a short across these wires or between them and the protection circuit will operate the alarm. Furthermore, three lamps are provided, one lighting whenever the control switch is in the "test" position, another when the selector switches are set for full protection, and the third when the protection circuits are complete, all lamps going out when the control switch is set to "protection". The protection circuit leads may be run in conduit across windows and the like or passed to-and-fro over door panels so that wrenching out windowbars or cutting door panels would sever the circuit. To allow an authorised person to leave without actuating the alarm a time-delay switch may be provided, and to allow authorised entry a disguised switch connected across a certain detector switch may be fitted. According to the second Provisional Specification, the control switch may be fitted to a skirting board and disguised as a three-pin power plug socket ; also the main control box may be situated on an inside wall directly behind the external alarm casing, the two being coupled through the wall by a steel tube carrying the connecting wires.