Introduction to Polygraph Machine

A polygraph (popularly referred to as a lie detector) is an instrument that measures and records several physiological responses such as blood pressure, pulse, respiration, breathing rhythms, body temperature and skin conductivity while the subject is asked and answers a series of questions, on the theory that false answers will produce distinctive measurements. The polygraph measures physiological changes caused by the sympathetic nervous system during questioning. Within the US federal government, a polygraph examination is also referred to as a psycho physiological detection of deception (PDD) examination.


Polygraphs are in some countries used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. The use and effectiveness of the polygraph is controversial, with the manner of its use and its validity subject to increasing criticism.