A polygraph (popularly referred to as a lie detector) measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions. The belief is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers.
The polygraph was invented in 1921 by John Augustus Larson, a medical student at the University of California at Berkeley and a police officer of the Berkeley Police Department in Berkeley, California. According to Encyclopædia Britannica, the polygraph was on its 2003 list of greatest inventions, described by the company as inventions that "have had profound effects on human life for better or worse."
Many members of the scientific community consider polygraphy to be pseudoscience. Nonetheless, in some countries polygraphs are used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. US federal government agencies such as the FBI and the CIA and many police departments such as the LAPD use polygraph examinations to interrogate suspects and screen new employees. Within the US federal government, a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination.
Read more about Polygraph: History, Testing Procedure, Validity, Countermeasures, 2003 National Academy of Sciences Report, Use With Espionage and Security Clearances, Hand-held Lie Detector For U.S. Military, Use With Sex Offenders, Polygraphy in Popular Culture