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The E-meter is even less useful than a polygraph. For those wondering, it is used in some situations by the church of Scientology, to asses people's motivations - a sort of very crude lie detector test
The circuit for the first ones is in the public domain, being part of L Ron Hubbard's patent.
The new ones include a mains supply and some more electronics, to reject picked up mains hum and proved some filtering for false alarms but the functions are the same.
link to site with a tear down.
It will not work correctly unless you feed it with the correct type of arc or surge though, so beware of false readings!