Abstract: An audio indicator apparatus for locating boundaries of optically divided detection zones covered by a passive infrared detection system having a collector for collecting infrared rays from the zones of an area to be monitored, and a detector for passively detecting infrared rays collected by the collector and for generating a first signal having an amplitude responsive to the rays collected by the collector, which includes a signal generator to be connected to a speaker for producing a second signal responsive to the first signal, the second signal being indicative of activity of the detection system at a point, within the area to be monitored, where an infrared radiation emitting object is moved, to locate the boundaries of the zones.

Abstract: A smoke and fire detection system wherein a central controller transmits data to remote transponders on a voltage supply line by pulse code modulation (PCM) of the supply voltage, and the transponders communicate with the controller by pulse width modulated (PWM) current pulses over the voltage supply line. A transmitter in the controller supplies a nominal operating voltage to the transponders and transmits a data word comprising a plurality of data bits to the transponders over the line. The transmitter generates each data bit by switching the voltage supplied to the line from the nominal operating voltage to a first voltage corresponding to a first logical level or a second voltage corresponding to a second logical level. A decoder in each transponder derives the transmitted data word.