Polygraph tests, or lie detector tests, measure a variety of physical attributes to determine if a person is lying or not. Commonly, polygraph tests will measure changes blood pressure, heart rate, breathing rate and amount of perspiration, or sweat, in relation to the questions being asked. Most polygraph tests will start with basic questions, such as confirmation of name and address, to establish a base line reaction. While polygraph tests are featured widely in television shows and movies, they actually are not used that commonly in real life criminal proceedings.
In most states, polygraph tests are inadmissible in court. Polygraph results are inadmissible because it does not pass the Frye Test. The Frye Test states that polygraph evidence needs to be acknowledged by the general scientific community as accurate, to have a qualified test conductor and to be proven that proper procedures were followed. Because the scientific community does not agree on the accuracy of polygraph tests, the tests are generally not allowed in criminal proceedings. However, some states, including California, Arizona, Georgia and Florida will allow polygraph results in court, only if both parties allow for the test to be administered and the results to be revealed. In all other states, polygraph results are inadmissible in court unless there exists a rare and unique set of circumstances that convinces the judge to allow the polygraph results.
While polygraph tests are mostly inadmissible in court, they can still be used by the police and other law enforcement groups during the course of an investigation. Polygraph results are sometimes used by law enforcement to establish probable cause in order to obtain a search warrant. While the polygraph results cannot be used in court, evidence found through the search warrant would be able to be presented. Anyone subjected to a lie detector test by law enforcement should consult with a defense attorney first.
While polygraph tests are used widely in the media, the truth is that these test results are generally banned from courtrooms in criminal proceedings because of their unreliability. Law enforcement, however, can still use polygraph tests in order to obtain warrants, which may lead to admissible evidence.