The device developed by the author consists of three units, one recording continuously and quantitatively the subject's blood pressure and pulse, one giving a duplicate blood-pressure pulse curve taken from some other part of the subject's body, and the third recording respiration. The success of this device in detecting deception and guilt on the part of criminal suspects was attributed in large measure to the psychological effect such a test has in bringing about confessions. An estimated 75 percent of guilty suspects who had undergone the test as of the original writing of this article had confessed to their crimes. To ascertain the physiological responses resulting from deception, the author performed an experiment which eliminated the fear and anger features normally accompanying criminal deception. Other experiments focused on the determination of guilty or true deception.