A polygraph or lie detector test
records a subjects physiological responses while answer a series of questions. Do they tell necessesarily if somebody is lying? No. They do however notify the tester when the person exibits signs associated with the physical changes the occur when somebody is lying. This homemade lie detector isn't nearly as scientific as professional grade machines, nor are you a trained test administrator. Still, if you're looking to have a little fun, build a working polygraph machine and catch a lier then you'll enjoy this project.
The circuitboard assembly looks fairly complicated. You'll need some understanding of electronics, but the video has a helpful diagram and instructions. The video also shows this homemade polygraph in action. It measures the skin resistance which goes down when the subject is lying. If you want to back up your test with some behavioral science, check out M.E. Williams post on How to catch a liar in the act
. I wouldn't do anything drastic based on the results of a homemade test, but it does sound like a fun experiment. Maybe you'll find out what people really thought of your Thanksgiving dinner?