How does Lie Detector works.?
Answer:
It measures blood pressure, breathing and sweat activity. It is certainly not foolproof.
There is not much evidence at all that it can detect lies. It is mainly used as an interrogation tool. If a suspect thinks the lie detector works, then he might confess.
The quickest answer is "They don't".
A lie detector is really an anxiety detector. A number of people support themselves teaching others how to beat a lie detector.
A lie detector is more properly called a polygraph. At a minimum, a polygraph consists of blood pressure, pulse, respiration, and galvanic response, because when you are stressed, your heart pounds, you hold your breath, and you sweat. Most polygraphs are of this simple kind, and combined with inexpert examiners, are about as good as a coin flip. Better polygraphs, equipped with such tests as temperature of extremities, run by highly-experienced operators, may be more effective - or perhaps it is the human, not the equipment, that is detecting the lies.
There's a story floating around the internet about cops putting a metal colander on a suspect's head, and whenever they thought he was lying, they hit the button on the xerox machine, and a piece of paper popped out, saying, "He's lying". Supposedly, the guy was scared to death, and confessed. I remain skeptical, but concede the possibility that the perp was a real doofus.
About 20 years ago, another form of lie detector emerged, which analysed voices for stress. Instead of asking questions which are answered yes or no, the subject merely talks, and he doesn't even have to know he's being analysed. Initial demos of the equipment, for instance, used recordings of politicians talking. The voice stress analysis was so sensitive, that it could detect which words concealed the truth.
For instance, a polygraph operator would ask, "Are you in love with Miss Feeney?" and the subject has to answer yes or no. The voice stress analyst, however, would note that the "I" in "I love Miss Feeney" is stressed, indicating that it's someone else who loves Miss Feeney, or the "love" is stressed, indicating that he'd not sure it's love, or "Miss" is stressed, indicating that perhaps Rosalyn Feeney is secretly married, or "Feeney" is stressed, indicating that the subject is having an illicit affair with our Miss Brooks, instead of Miss Feeney.
Voice stress analysis is widely used in police and insurance investigations, but neither it nor polygraph results are admissible in court, a recognition of the fact that they are controversial techologies not widely accepted by the scientific community as being valid.
hey dude a lie detecor basically reads your blood pressure,heart beat and your sweating rate and matches it to the normal one which is taken before you are subjected to the lie detection test
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