GB1335707A - Alarm system particularly to counter shoplifting - Google Patents

Abstract

1335707 Theft alarms I J YOUNG (INSTALLATIONS) Ltd 16 Nov 1971 [19 Aug 1970] 39943/70 Heading G4N A theft alarm system comprises a closed container housing a mains transformer T1 feeding a rectifier REC1 which supplies power to a relay RL1 via a pair of sockets SK2, SK4. Socket SK4 is connected to a switch contained in a pedestal so that the switch is opened by removing an article from the pedestal. As described, the system is reset by operating pushbutton SW2 which energizes relay RL1 via a breakable flexible conductor linking SK2 and the pedestal switch connected to SK4. The relay RL1 is held energized by contacts 4 and 5 but released by rupture of the flexible conductor or removal of the article from the pedestal, so as to operate an alarm bell BL and indicator lamp PL2. A further buzzer is operated by relay RL2 in the event of supply failure. Fig. 7 shows an arrangement having three switches S contained in one or more pedestals, each switch being set to its upper position when an article(s) is removed from the pedestal. The momentary open circuit thus releases relay RL1 and sounds the alarm bell BL. A further alarm lamp BL3 is energized via isolating diodes D. The alarm can be inhibited by an authorized person using a key comprising a magnet to operate a read contact unit 22 and a probe to close contacts 20. Modifications.-Relay RL1 may be replaced by a thyristor whilst the bell BL may be replaced by a transistorized oscillator emitting one frequency for power failure and a second frequency in response to theft.