FireAngle Thermistek Heat Alarm is a predictive technology monitors the rate of temperature increase and alerts you to the danger quicker. Thermistor heat sensing element for accuracy, reliability and stability. Heat alarm for use in places where a smoke detector is not suitable, for example where there are high ambient air temperatures, high humidity or in dusty and dirty environments. e.g. garages, lofts and kitchens. 10 year sealed in power pack removes the need to replace the batteries.