Scientology Mark V E-meter. Serial number: Delta 3950. It was last calibrated in 1978, but that’s ok, it still does nothing useful just as well as a "modern" Mark VIII Quantum right off the rack.
This device would be attached to two metal cans held by the subject. A mild current is passed through the body, and the electrical resistance across their body is measured. The conductivity of human skin varies depending on a variety of factors, such as the relative wetness/dryness of the palms. Scientologists believe it measures a variety of things, from prior psychological trauma, to deceitful intention. In "Sec Checks", the device is used more like a primitive polygraph machine to interrogate the subject. This can go on for months to years, as long as it takes to secure a confession victims of the process.
via Flickr http://flic.kr/p/wxUwug
The Random Treasures of an Insignificant Nobody 