They of course aren't very accurate, and really shouldn't be relied upon in anything more critical than daytime television. But you can use techniques to attem

They of course aren't very accurate, and really shouldn't be relied upon in anything more critical than daytime television. But you can use techniques to attempt to make them more revealing. The first obvious one is to simply convince people they work, and then use them as a persuasion technique. "Look, do you want to just come clean here or are we going to have to bring out the polygraph?" The second technique you can use is to ask a series of alternate fact questions and look for response. "Did the murder happen at five o'clock? Did it happen at six o'clock? Did it happen at eight o'clock?" Somebody who is doesn't know the answer isn't going to be any more nervous at any of those questions in particular, but someone who does is often going to have a nervous spike as, or just before, the correct question is asked.