Abstract: A transducer in the form of a long cable for producing electrical signals in response to mechanical vibration of the cable. The cable comprises an elongate magnetic member and an electrical conductor extending alongside the magnetic member, the electrical conductor being loosely mounted in the magnetic field of the magnetic member so that mechanical vibration of the cable causes the electrical conductor to move relative to the magnetic field whereby an e.m.f. and hence an electrical signal is induced in the conductor. The transducer may be used in monitoring or security apparatus.