Smoke Detection Measures the number of smoke particles in the air. Photoelectric & Ionization smoke detectors are used here. Heat detection Measures the rise of temperature within a given interval and the maximum temperature. This group includes rate-of-rise temperature detectors and fixed-temperature heat detectors. Flame / Spark detection Measures the radiation stemming from the fire (infrared, visible, ultraviolet). Infrared and ultraviolet flame detectors are mainly used in this instance.