Abstract: Alarm or warning device using, as sensing means, a low voltage D.C. biased shielded coaxial cable. The cable is positioned along the periphery of the area under control, and one or both of its ends are connected to an electronic circuit adapted to detect the voltage variations at the cable ends, deriving from its capacity variations resulting from the subsonic shock waves caused by the movement of things or people in the neighborhood of the cable. The device of the invention is used in alarm systems against intrusions and thefts, both for real and personal property. In the first case, it is preferably positioned underground and it may also comprise screening means allowing to detect the movements coming from different directions. The device is also advantageously used in the medical field, for the remote control and warning of the life functions of a patient.