Viet Cong Detector

  I served in Vietnam during 1967/1968 with the 4th Infantry   Division located in the Central Highlands near Pleiku.  While   serving with the AG Division, I learned that the Division had a   homemade Viet Cong
  Detector in the form of a handcrafted box with switches,
  wires, etc which was routinely taken to nearby villages that
  had volunteer VC informers. I managed to obtain a copy of
  the diagram and instructions.
  (src="https://www.war-stories.com/images/chronister-vc-detector-1-1967.jpg" target="_blank">Click diagram for full size)

  I never witnessed it's actual use but I did hear that it was very
  impressive, and is a very interesting story.

  SFC John Chronister
  NCOIC, Awards and Casualty Branch

 [Discussing the above further, the way it would work would be to have an informant in the village, concealed, but where he could see the detector. Then you would announce all the men had to walk between the boxes and if the lights light up he was a Viet Cong! Of course the informant would push a button when a known-to-him VC walked near the detector. Pretty soon, the young men would take off running. The gadget apparently worked effectively for a while, but the temptation for an ugly informant to better his odds with the ladies as the only man left in town could prove too tempting. Heh-heh.]