GB1422619A - Burglar alarms - Google Patents

Abstract

1422619 Burglar alarm systems ELECTRICITE DE FRANCE 6 Sept 1973 [14 Sept 1972 21 Aug 1973] 41946/73 Heading G4H In a burglar alarm system, a plurality of transmitters are located in respective installations to be guarded and each is controlled by one or more respective burglary detection devices to transmit, using a common frequency, a coded signal representative of its respective installation, there being at least one continuously-operable control receiver comprising a substantially omni-directional aerial and a selective rotary aerial. Reception of such a coded signal at the central receiver through the omni-directional aerial gives an audio/visual alarm and the signal is recorded. To avoid conflict between different transmitters sending simultaneously, an operator at the central receiver can cause the circuits to be fed instead from the rotary aerial and the latter to be rotated through one (or two) revolutions, spikes being recorded on a chart recorder as the aerial aligns with the active transmitters, the directions of the transmitters being read by the operator from a scale alongside the chart. The operator then turns a knob to align the rotary aerial with the active transmitters in turn, using a selsyn, to enable the codes therefrom to be recorded. This alignment could alternatively be automatic.