The HDC sensor cable detects heat anywhere along its length:
it is a continuous heat detector, unlike the standard point detector.
The HDC sensor cable is composed of two copper-covered steel wires, individually insulated with a thermosensitive polymer.
At the rated temperature the polymer insulation melts, thus permitting the conductors to short-circuit and generate an alarm signal.
Four temperature alarm levels are available: 68 °C, 88 °C, 105 °C and 138 °C.