3 Answers

Is the lie detector test (polygraph) accurate? That depends on who you ask. Studies show results of all sorts. A recent Department of Defense Polygraph Institute study, found one experiment in which less than 37% of test takers who were non-deceptive were classified as such. Others were either classified as "deceptive" (false-positives) or "inconclusive." Would you really want to "prove" your innocence using a test with those odds?

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Colleen

The lie detector machine has been known to be beaten by a liar too.

Lie detectors cannot actually identify lies; all they can do is detect certain activities of a person’s body that are usually associated with lying: abnormal perspiration and flushing of the face, rapid breathing, increased heartbeat, and excessive swallowing.

Because this method does not actually guarantee the truth, the results are not generally accepted as evidence in court.
Although each of the body changes, alone, does not necessarily indicate a lie, when put together, they can provide an indication of one.

When a person is given a lie detector test, various parts of the machine are attached to his body, and a written record is made of his answers. Usually, three or four tests are given to be sure that the answers were not accidental.

Yet, amazingly enough, a lie detector can be fooled! There are some people who are truly unaware that they are lying. These people cannot be caught by a lie detector.

Yes.  Lie detector machines have been proven to be pretty reliable at detecting physiological characteristics consistent with lying.  Likewise, some people are trained to spot both verbal and non-verbal clues consistent with lying.  Finally, most liars are often caught by their own mistakes, such as telling two different stories to different people, or at different points in time.  The bottom line is lying is wrong, so don't do it.