Pros and Cons of Lie Detectors


Lie detectors measure an individual's pulse rate, body temperature and perspiration as signs of an attempt to deceive. While the technology is subjected to intensive scrutiny throughout popular media and defense attorneys echo these concerns to discredit the use of polygraph machines on their clients, lie detector tests are still used under various conditions because the technology can be effective.

Law Enforcement

  • Claims that lie detector tests are unreliable are overstated. Polygraph technology is generally reliable except in cases where severe manipulation of the technology is taking place. The results of a lie detector test are not considered reliable enough in a court to force a conviction by itself; however, they are still admissible as evidence and help both law enforcement and defense attorneys form their relative cases.

Controlled Environment

  • Lie detector tests are performed in a carefully controlled environment where clear questions are posed to a suspect and answered with equally clear answers. They allow law enforcement officers to question a suspect in a controlled environment for the purposes of obtaining a clear statement, says the Burbank Law Firm. The actual results of the lie detector test are less important than the statement itself. The statement received through the process of taking a lie detector test is admissible as evidence, even if the results of the test are not.

Conditioned Fear

  • Everyone has some amount of a conditioned fear toward lie detector tests. This can come from watching movies, television shows and reading books filled with intense scenes where lie detector tests are used to catch and convict suspects. While the reality of lie detector tests is different, the fear remains. This fear, combined with the stress of police questioning and the controlled environment of a lie detector test, leads to unpredictable physical responses from test takers. Heightened blood pressure and an increase in pulse and body temperature are all symptoms of a high stress environment that can lead to false positives on a lie detector test.


  • Lie detector tests rely on a machine that tracks physiological changes in a person's body as a result of specific questions by an examiner. An examiner can manipulate a test's results by using careful questioning techniques or by intensive conditioning of a subject. A subject also can manipulate the results by using sedatives and antiperspirant to emulate a calm, relaxed persona, says the Electronic Private Information Center. This potential for manipulation on both sides renders the results of any polygraph test suspect, at least enough for most lawyers to reject their use on their clients.


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