The 120-Volt Hardwired Heat Alarm detects heat at 135F with its (microprocessor) temperature sensor. This heat alarm is perfect for crawl spaces and garages and has a low battery silencer for a maximum of 8-hours. First Alert invests time and research into providing dependable and hardworking products. The HD6135FB comes in white and can be interconnected with up to (12) other units to make your home a safe haven from fires and smoldering fumes. The alarm automatically resets when temperatures drop under 130. Its indicator lights are easy to understand - constant green means power is on, intermittent green means the battery is being used and rapid red is a local alarm. The 120-Volt hardwired Heat Alarm keeps your family and valuables safe from the dangers of heat. Committed to innovation and value, First Alert improves safety in and around the house.