Well, "lie detector" was a misnomer from the start, and is of dubious value in many cases. Was another subject covered in the class.
The proper name- polygraph- is not a negative in any way, however- and is quite accurate a description. It graphs (reads, stores, writes, manipulates, etc) poly (multiple) physical properties of the body. The whole idea of it being a lie detector was that if you lie your stress level increases, and can be sensed.. Obviously a flawed idea from the start. Sociopaths and psychopaths both feel no stress when lying,, and those are who you are trying to catch.
Biofeedback is an awesome subject, and leads you down a lot of cool thought paths that can even be prototyped with our favorite little toy,...
One warning though, must be made. Take EXTREME care when dealing with electricity and the body. One mistake can kill. Everything battery powered, no mains, isolated as much as possible, measure every voltage and current at every contact point to make sure, etc etc etc. I'm sure there's a few darwin awards that started out as tinkering, don't become one! 