I attended a corporate security seminar a few years ago where the lie detector was demonstrated and explained. The true intent of the polygraph is to scare the suspect into confessing. It's a deceptive tool of investigation and the results are subjective. If three testers give the same person a lie detector test, the suspect might pass one and fail two, pass all three, fail all three, etc. In the past the person administering the test would sometimes use card tricks, number games etc. to "prove" the effectiveness of the test to his/her mark. Most criminal defense attorneys and people in the know will advise you against taking a polygraph, regardless of guilt or innocence. It's utterly insane that anyone would even suggest having this type device at a security checkpoint. Lie detectors prove NOTHING, except for how quickly people are to give up their rights and help career minded hacks build a case against them. My policy has always been to say as little as possible to those who would want to use me as another "notch in their belt." This applies to TSA screeners, traffic cops, CBP, etc. It makes little difference if you are doing something "wrong." There are many unscrupulous individuals who would gladly build a case against you, guilty or not. Prisons are full of people, some of whom were innocent and thought they'd be ok by "telling the truth." Don't waste your time and if ever you see the polygraph, tell them politely to "Shove it."