Heat detectors are the oldest type of automatic fire detection device. Heat detectors feature a detecting element inside the unit that activates when it reaches a predetermined fixed temperature or when a specific increase in temperature has occurred. Heat detectors are best suited for:

applications where detection speed is not a prime consideration or where ambient conditions would not allow the use of a smoke detector fire detection in small, confined spaces where rapidly burning, high heat fires are anticipated

Heat detectors have a lower false alarm rate, but they are also slower than smoke detectors in detecting fires. Studies have shown that heat detectors are not as effective as smoke detectors in detecting fires in residential homes.