The Kidde HD135F is a 120 VAC wire in heat alarm that responds to temperature rather than smoke. The alarm will sound if temperatures rise above 135 deg F. The Kidde HD135F is interconnectable. The interconnect system must not exceed the NFPA limit of 18 initiating devices (smoke, heat, CO, etc) interconnected, it is still possible to interconnect 6 strobe lights and or relay modules.