Abstract: A fire detection system includes a single conductor pair for both supplying the energizing voltage to all of the fire detectors in the protected area and receiving back status information regarding the individual detector operation. The system provides individual, successive alarm outputs to regulate successive functions such as "evacuate the area", "dump the fire extinguishing material", and "call in the local fire department", as successive ones of the detectors are alarmed. The system includes a voltage regulator for supplying a well regulated voltage to the detectors, which regulator is switched into a current limiting mode to prevent an inaccurate first alarm signal if the conductor pair is short circuited. This system also provides a trouble-indicating output signal if the system loses supply voltage or experiences a ripple voltage beyond a preset amplitude.