The present invention relates to the taut wire type intrusion detection system for detecting an unauthorized intrusion into a restricted area.  The invention also relates to detector devices particularly useful in such intrusion detecting systems. 
Many types of intrusion detectors and detection systems have been developed or proposed, including electrical switches mounted on a fence to detect any disturbance (e.g. cutting or moving) of the fence, photocell devices which detect the attempted intrusion by the interruption of a light beam, and antennae systems which detect the intrusion by the unbalancing of an electrical field in the area to be protected.  As the need for such intrusion detection systems increases, efforts are continuously being made to decrease their cost and to increase their reliability.