The Kidde HD135F is a 120VAC Wire In Heat Alarm that responds to temperature rather than smoke. The alarm will sound if temperatures rise above 135ËšF. The Kidde HD135F is interconnectable. The interconnect system must not exceed the NFPA (National Fire Protection Association) limit of 18 initiating devices (Smoke, heat, CO, etc) interconnected, it is still possible to interconnect 6 strobe lights and or relay modules. This unit includes a 5-year limited warranty and is UL Listed.