A device that detects a preset high temperature or a rapid rate-of-rise (ROR) in temperature. Heat detectors can be either electrical or mechanical in operation. The most common types are thermocouple and electro-pneumatic, which both respond to changes in ambient temperature. If the ambient temperature rises above a predetermined threshold, then an alarm signal is triggered. Heat detectors are often placed in rooms where smoke would normally be found such as a kitchen or smoking lounge.