Gelbau Safety strip, T-foot, black, 230V, (Sold per m) 20mThe sensing strips consist of two layers of rubber, one with conductive and one normal insulating rubber. A copper wire embedded in two separated layers of conductive rubber together with a resistor at the end of the sensing strip, forms a closed circuit. If the separated layers are pressed together there is a short circuit, the control unit react and its outputs release. In the same set hammer the control unit reacts to an open circuit in the cable