Why Is a Lye Detector Test Not Acceptable in Court?



Police officers often pressure suspects to take a lie detector test. Although the Supreme Court has left it up to individual jurisdictions to outlaw or allow its use, the results are rarely admissible in court.

The test works by recording physiological indicators of lying, such as breathing changes, sweat gland activity, and heart rate. However, such indicators can also be a sign of anxiety or excitement.


When someone is charged with a crime, they often find themselves being asked to take a polygraph test. While it may seem like the polygraph could take the guesswork out of determining whether or not someone is lying, it is important to remember that the results can be inaccurate and that it is not in your best interest to agree to one without first consulting a criminal defense attorney.

The first thing to keep in mind is that the polygraph machine relies on a person’s physiological responses to questions. The machine can detect a variety of things, including heart rate, perspiration and blood pressure. This is how the machine determines if someone is telling the truth or not.Get more info on this Lie Detector Test website.

The problem is that many of these reactions are caused by stress, anxiety and other emotions. A person who is being questioned by police and prosecutors about something that they did not do may be incredibly stressed and experience an increase in these symptoms. These changes can make it appear as though they are lying even when they are telling the truth.


Polygraph tests are commonplace in television crime dramas, and it might seem like they can take the guesswork out of determining whether a person is lying. However, most courts do not consider polygraph results admissible in court.

The main reason is that people’s reactions to questions can differ based on their emotional state. For example, if someone is nervous or stressed out while taking the test, their heart rate and blood pressure might rise. This could lead the examiner to believe that they are lying.

In addition, there are a number of ways that people can beat a polygraph test. These methods include biting one’s tongue or putting a tack in the foot to affect blood pressure and perspiration levels. Many of these tricks, however, can confuse the machine and result in a false positive. Ultimately, this can cause innocent people to be falsely convicted.


Because of the doubts about their reliability, most courts have per se rules against admitting lie detector test results. In addition, the Employee Polygraph Protection Act prevents most private employers from requiring employees or job applicants to take a polygraph and from taking action against them for refusing.

The problem with polygraphs is that there are many ways to skew the results. For example, if someone is nervous during the test, their blood pressure will go up, making the examiner think they’re lying. Other tricks that can change results include taking sedatives to minimize anxiety, applying antiperspirant to counteract sweating, and holding one’s breath between questions.

As such, a defendant may be able to use their own prior inconsistent statements against them in court for impeachment purposes. However, the witness must have a reliable source of this extrinsic evidence. If the inconsistent statement is written, it can also be used for impeachment purposes.


Polygraph results are suspect at best, and even if they were admissible in court, they could be used to persuade jurors that the defendant is guilty of a crime. However, despite their unreliable nature, police and prosecutors often pressure people to take the test.

One of the main reasons for this is that they believe a person will admit their guilt if they refuse to take the test. In addition, they may tell them that the test will show that they are lying, and the fact that they are being interrogated means they should confess.

There are also a number of medical conditions that can make a person ineligible to take the test, including epilepsy, nerve damage (including essential tremor), heart disease, and mental illness. Additionally, some medications can skew the results. For this reason, it is important to consult a criminal defense attorney before agreeing to a polygraph test.