Fire detection system with multiple output signals

A fire detection system comprising:

• two, and only two, conductors extending throughout an area to be protected;
• a plurality of fire detectors, each coupled between the conductor pair at different physical locations throughout the area, and each of which signals an alarm in the same manner, by presenting a low impedance across said conductor pair;
• termination means exhibiting a capacitive reactance and coupled to the end of said conductor pair;
• a control unit connected to supply a d-c potential difference between said conductors;
• and
• circuit means in said control unit, coupled to said conductor pair to receive detector status information over the same two conductors which pass the d-c energizing potential difference to the detectors, which control unit is effective to provide a first alarm output signal when the first one of the detectors is alarmed, and to provide a second alarm output signal when any of the remaining detectors is subsequently alarmed.