Abstract: Detection apparatus comprising a plurality of elongate transmitting conductors each coupled to a source of electromagnetic energy and arranged for producing an electromagnetic field along the length thereof, at least one receiving conductor arranged alongside the plurality of transmitting conductors for sensing the electromagnetic field produced thereby, and alarm indicating circuitry coupled to the at least one receiving conductor for providing an alarm indication in response to a sensed disturbance of the electromagnetic field, the source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by the transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of the transmitting conductors.

Abstract: A protective system employing vibration sensors for indicating the location of a vibration or of tampering with the system. There is employed a vibration sensor comprising first apparatus operative when the sensor is oriented in a first range of orientations for providing a momentary first impedance condition in response to vibration of at least a predetermined strength and second apparatus operative when the sensor is oriented in a second range of orientations for providing a steady state second impedance condition.