lie detector, instrument designed to record bodily changes resulting from the telling of a lie. Cesare Lombroso, in 1895, was the first to utilize such an instrument, but it was not until 1914 and 1915 that Vittorio Benussi, Harold Burtt, and, above all, William Marston produced devices establishing correlation of blood pressure and respiratory changes with lying. In 1921 an instrument capable of continuously recording blood pressure, respiration, and pulse rate was devised by John Larson. This was followed by the polygraph (1926) of Leonarde Keeler, a refinement of earlier devices, and by the psychogalvanometer (1936) of Walter Summers, a machine that measures electrical changes on the skin. A more recent innovation are devices, first developed in 1970, called psychological stress evaluators or voice stress analyzers, which measure voice frequencies from tape recordings.
Although the lie detector is used in police work, the similarity of physical changes caused by stress and such emotional factors as feelings of guilt to changes caused by lies has made its evidence for the most part legally unacceptable. An assessment of such devices by National Research Council (an arm of the National Academy of Sciences) found that they also were too unreliable to be used in screening for national security purposes, but they are widely used for such purposes nonetheless, sometimes with inconsistent results from one government agency to another. The use of lie detectors to screen employees and job applicants is highly controversial.
See E. B. Block, Lie Detectors, Their History and Use (1977); C. Gugas, The Silent Witness (1979); D. T. Lykken, A Tremor in the Blood (1981); K. Alder, The Lie Detectors: The History of an American Obsession (2007).