A popular name for a polygraph which tests the physiological reaction of a person to questions asked by a testing expert. a potential or actual criminal defendant or possible witness cannot be forced or ordered to take a lie detector test. some habitual liars pass lie detector tests, and innocent, honest people fail them due to nervousness and other factors. however, law enforcement authorities usually believe the results, which occasionally exonerate (clear) a suspect. since the results are sometimes unreliable, they are not admissible in a trial and may not be referred to.