The 55000-193 Apollo Alarmsense Heat Detector is specifically designed to be used on Apollo Alarmsense Two Wire Fire Alarm Systems.  This detector is a High Heat type Heat detector which can be used on two wire fire alarm system circuits along with sounders and beacons on the same circuit.

The 55000-193 Apollo Alarmsense CS high heat detector operates by using a matched pair of thermistors to sense heat. One thermistor is exposed to the ambient temperature, the other is sealed. In normal conditions, the two thermistors register similar temperatures, but, on the development of a fire, the temperature recorded by the exposed thermistor will increase rapidly, resulting in an imbalance of the thermistors and causing the detector to change to the alarm state.