Heat detectors are used to sense a change in the environmental temperature caused by a fire

All heat detectors listed for fire detection have a fixed temperature set point. That is the temperature at which they will activate and signal back to a control unit. It is important to note that the fixed temperature is the temperature of the detector. not the temperature of the fire gases

As the hot fire gases flow across a heat detector. The element absorbs the heat and increases in temperature. This spot-type heat detector is nonrestorable. If it reaches its operating temperature. The solder melts. allowing the contacts to close. This signals that the detector has activated

heat detector can be restorable or non-restorable type .and can work in fixed or Rate of Rise temperature