Abstract: In a taut wire type intrusion detection system, each parallel wire defining a section of security fence is tensioned between a pair of wire-supporting vertical anchor posts. Intermediate the anchor posts there is provided a row of regularly spaced vertical detector posts each presenting a plurality of individual sensors, each associated with one of the taut wires and operable to produce a sensor signal when the tension of the wires changes. With each detector post there is associated sensor signal processing means, operable to analyze the sensor signals produced by the sensors of the detector post in response to changes in tension of the taut wires, and to generate output signals correlatable with the sensor signals. Each sensor preferably includes a pressure transducer comprising a partially conductive compressible elastic sensing element whose resistance changes with applied pressure.