Signaline HD, unlike fixed temperatures, does not have a pre-determined alarm temperature. Instead the cable detects a rise in temperature. This is achieved via the associated controller continually measuring the resistance within the cable. The controller will provide a Class C response in accordance with EN54 standard for heat detectors. Unlike Signaline FT, Signaline HD does not need to be replaced once it has alarmed. Once the cable has cooled it is completely resettable