A polygraph, or a lie detector test as its most commonly known, is a complex device that measures perspiration, blood pressure and heart rate. The way that it works to tell people if you are lying is through careful examination of these physiological reactions and how they might change depending on different lines of questioning. An examiner asks certain control questions, usually some where it’s certain the interviewee will be telling the truth and some where he is asked to lie, and then works up to asking him the question where they want honest answers.

The device is not foolproof. Many detractors claim that a polygraph has only 50 -65 percent accuracy in determining the honesty of someone’s answers. While proponents claim that it has a 90 per cent success rate. The real accuracy of these machines is most likely somewhere in the middle, but they remain an incredible, and the only, tool for law enforcement to put pressure on suspects and help them get at the truth.


Different States, Different Laws

The fact that opinions on the accuracy and reliability of polygraphs remains disputed by many means that different states have constructed different laws regarding their use by police offices and courts.  Legal Match asserts that, “Almost every state fits into one of two categories; those that find them completely inadmissible and those that allow their admission with “the stipulations of both parties” (meaning both you and the prosecutor agree to admit the test results as evidence).


Case History

In the US Attorney’s Manual the reasoning fro this dates back to a case in 1923, Frye v. Unites States, in which the results of a polygraph were deemed inadmissible. However, in 1997 the case US v. Cordoba resulted in the decision to allow some results if the polygraph is used in conjunction with a witness and all parties agree. Most interestingly, the manual states that , “…there is no bar to the introduction of voluntary incriminatory statements made during a polygraph examination.” Meaning that the results of the lie detector test may not be important, but what is asked and said during the test could still be.

If you live in New York, Texas, Illinois, Pennsylvania, and many other states, the results of a polygraph will never go to court. In California, Arizona, Nevada, and Florida, they might under certain circumstances. But, everyone should be aware that the polygraph is first and foremost an interrogation device and whatever is said during the test can and will be used against you no matter where you live.