How to Pass a Lie Detector Test

Tips for Beating a Polygraph Test

Close-Up View Of Lie Detector
A modern lie detector test compares blood pressure, breathing, and pulse rate when the subject is telling the truth and telling a lie. Andrea Nistolini / EyeEm / Getty Images

A polygraph test or lie detector test is designed to analyze physiological reactions to questions to determine whether or not a subject is being truthful. The accuracy of the test has been widely contested by groups including the National Academy of Science, US Congress Office of Technology Assessment, and American Psychological Association. Even so, the test is routinely used to screen employment applicants and interrogate criminal suspects.

While a person may be told to answer all questions honestly, the test is designed to measure responses to "white lies," which means truly honest people run the risk of generating false positive on the test. Other people may wish to conceal answers to certain questions, whether guilty of wrongdoing or not. Fortunately for them, it's not that hard to beat a lie detector test. The first step to passing the test is understanding how it works.

How a Lie Detector Test Works

A lie detector test includes more than the time spent hooked up to the polygraph machine. The tester will start making observations the instant a person enters the test center. A skilled polygrapher will notice and record nonverbal cues associated with lying, so it's a good idea to know your "tells".

The polygraph machine records breathing rate, blood pressure, pulse rate, and perspiration. More sophisticated machines include magnetic resonance imaging (MRI) of the brain.

Physiological responses to irrelevant, diagnostic, and relevant questions are compared to identify lies. Questions may be repeated two to three times. The subject may be asked to intentionally lie to help the examiner establish baseline values. The test typically requires one to three hours to complete, including the background assessment, medical history, explanation of the test, actual polygraph, and follow-up.

Tips to Beat a Lie Detector Test

The internet is filled with advice on ways to beat a lie detector test, but many of these ideas aren't very effective. For example, biting your tongue or putting a tack in your shoe to use pain to affect blood pressure won't affect perspiration levels. Similarly, imagining a lie when telling the truth and imagining the truth when telling a lie won't work because it establishes differences between lies and truth. Remember, differences between the truth and lies are the basis for the test! If you're unconvinced most advice is faulty, you may wish to review the Mythbusters lie detector experiment.

Basically, there are two good ways to beat the test:

  1. Be completely zen, no matter what you're asked. Note: Most people can't master this.
  2. Be completely distraught throughout the entire test.

Most people are nervous taking a lie detector test, whether they intend to lie or not. The physical responses to nerves probably won't fool a lie detector. You need to up your game to simulate feelings of mortal terror. This is because beating the test is all about mind games, which naturally affect physical responses. Here are some tips to try:

  1. If you want to beat the test, your best bet is to stay upset, fearful, and confused throughout the entire test. The goal is to appear calm and in control, despite the inner turmoil. Remember your worst experience or solve difficult math problems in your head — whatever keeps you in a constant state of excitation and stress. If there is one particular question you're worried about, imagine every question is that question before answering.
  1. Take time before answering any question. Identify it as irrelevant, relevant, or diagnostic (control). Irrelevant questions include asking you to confirm your name or whether the lights are on in the room. Relevant questions are the important ones. An example would be, "Did you know about the crime?" Diagnostic questions are ones most people should answer "yes" to but will most likely lie about. Examples include, "Have you ever taken anything from your workplace?" or "Have you ever lied to get out of trouble?"
  2. Alter your breathing during control questions, but return to normal breathing before answering the next question. You can make minor admissions here or not, as you choose.
  3. When you answer questions, answer firmly, without hesitation, and without humor. Be cooperative, but don't joke or act overly-friendly.
  1. Answer "yes" or "no" whenever possible. Do not explain answers, give details, or offer explanations. If asked to expand on a question, reply: "What more do you want me to say?" or  "There's really nothing to say about that."
  2. If accused of lying, don't fall for it. If anything, use the accusation as fuel to feel upset and confused.
  3. Practice any countermeasures before the test. Ask someone to ask you likely questions. Be aware of your breathing and how you react to different types of questions.

Keep in mind, applying these tips may enable you to invalidate the test, but won't be much use if you're taking a lie detector test to get a job. In most cases, the easiest way through a lie detector test is to approach it honestly.

Drugs and Medical Conditions That Affect Lie Detector Tests

Drugs and medical conditions may affect a polygraph test, often leading to an inconclusive result. For this reason, drug tests and a screening questionnaire are commonly given before a lie detector test. Medications that affect heart rate and blood pressure can affect polygraph results. These include antihypertensives and anti-anxiety medications and also a host of illegal drugs, including heroin, marijuana, cocaine, and methamphetamine. Caffeine, nicotine, allergy medications, sleep aids, and cough remedies may also affect the test.

While diagnosed sociopaths and psychopaths may be excluded from the test due to a potential ability to control responses, other medical conditions may prohibit the test. People who have epilepsy, nerve damage (including essential tremor), heart disease, have suffered a stroke, or are extremely fatigued should not take the test. Mentally incompetent people shouldn't take the test. Pregnant women are generally exempted from the test unless a doctor gives written approval.

With the exception of mental illness, drugs and medical conditions don't necessarily enable a person to beat a lie detector test. However, they do skew the results, making them less reliable.


  • Board on Behavioral, Cognitive, and Sensory Sciences and Education (BCSSE) and Committee on National Statistics (CNSTAT) (2003). "The Polygraph and Lie Detection". National Research Council (Chapter 8: Conclusions and Recommendations), p. 21.
  • "Scientific Validity of Polygraph Testing: A Research Review and Evaluation". Washington, D. C.: U.S. Congress Office of Technology Assessment. 1983.