A device intended to detect an involuntary physiological response that all persons exhibit when lying but never when telling the truth. Because there is no such specific lie response, the lie detector of popular fancy is mythological. In actual “lie protector” tests, widely used in the United States, breathing movements, blood pressure changes, and electrodermal responses are recorded on a polygraph while the respondent answers “yes” or “no” to a series of 8 to 12 questions. From the polygraph recordings, one can determine whether “relevant” questions had a greater impact on the respondent than did the interpolated “control” questions. In the standard lie test used in specific issue investigations, the relevant questions ask whether the respondent committed the act in question; for example, “On April 12, did you take $2000 from the office safe?” A typical control question might be, “In the first 20 years of your life, did you ever steal anything?” If the examinee reacts more strongly to the relevant than to the control questions, it is inferred that his or her answers to the relevant questions are deceptive. Because an innocent accused also may be disturbed by the relevant questions and react more strongly to them than to the controls, the lie test is biased against the truthful respondent. Research has shown that as many as 50% of innocent criminal suspects may “fail” control-question polygraph tests.