Security wire sensitive to any disturbance - uses resonance technique involving piezoelectric transducers

A security protection wire equipment, in which one or more security wires are sensitive to any small disturbances or to cutting, uses a mechanical resonance technique involving piezoelectric transducers. A wire (1) is stretched between two spring loaded terminals (6, 7) across the area to be protected, and acoustic or mechanical vibrations are induced and detected in and from it by two piezoelectric transducers (2, 3) one at each end of the wire. A feedback electric circuit, using another wire (10) is such that the whole network resonates at some natural frequency. Any change in this signal produced in the associated circuitry is detected, using a rectifier, integrator, comparator and relay and an alarm triggered if appropriate. An opto-electric transducer may be used in place of the relay.