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.