Are Lie Detector Tests Admissible in Court?

One of the greatest challenges for judges, juries, and law enforcement officers is determining who is telling the truth. This makes witness believability vitally important at a trial.

While witnesses must promise to tell the truth before taking the stand, judges and juries often hear conflicting testimony that indicates someone is lying. So, a lie detector test could theoretically help the jury determine the truth, but only if the test is reliable and can be used as evidence in court. It turns out that neither is true.

If you are under criminal investigation for potential criminal charges and are being pressured to take a lie detector test or you’ve already taken a test and are worried about it being used against you, contact an experienced criminal defense attorney to help you. Your attorney will be able to protect your rights and options for building a strong defense.

Are Lie Detectors Accurate?

In short: Lie detector tests have questionable reliability and are generally not admissible as evidence in court. They can be used in some investigations and for decision-making when applying to some federal employment positions.

It might seem like the technology of the lie detector test, also known as the polygraph test, could take the guesswork out of determining who is lying and who is telling the truth. That’s how many television crime dramas made them look. But the accuracy of lie detector test results can vary depending on the person administering the test, the machine used, and the person taking the test.

As such, polygraph results are generally not admissible in criminal cases unless both parties agree to it. Even then, some states do not allow polygraph tests to be used as evidence, and often a trial judge has discretion to allow (or not) a polygraph exam.

Those who are opposed to allowing the results of lie detector tests to be used in a court of law argue that jurors might accept the test results without considering the test’s accuracy or the threat of false positives. Jurisdictions that allow the results of lie detector tests in court also allow each party to present evidence as to why the test is or is not reliable.

Polygraph test results indicate physiological changes like the test taker’s heart rate differences using control questions like “What is your name?” and then more probing questions which would indicate alleged guilt or innocence.

What States Allow Polygraph Tests in Court?

The U.S. Supreme Court leaves the question of the admissibility of lie detector test evidence up to individual states. Other states do not allow any lie detector evidence.

The criminal justice systems of states that may allow the results of a polygraph test as evidence in a criminal case include:

• Alabama
• Arizona*
• Arkansas
• California*
• Delaware
• Florida*
• Georgia*
• Idaho
• Indiana
• Iowa
• Kansas
• Nevada*
• New Jersey
• New Mexico
• North Dakota
• Ohio
• Utah
• Washington
• Wyoming

States with an asterisk (*) allow lie-detector evidence in certain proceedings or only when both parties agree to its admissibility. In states where they are admissible, you could have expert testimony on your behalf about the unreliability of the test’s results.

The Argument for Lie Detector Admissibility

Those who think the use of polygraph evidence should be used in court say that the tests are reliable most of the time and, therefore, useful information. One argument is that the machine can pick up imperceptible changes in skin conductivity. However, many experts disagree with this assumption. Accordingly, in leaving the decision up to individual states, the Supreme Court commented that there is no reliable scientific evidence about the accuracy of lie detector tests.

How a Lie Detector Test Works

Essentially, the polygraph machine is attached to the person’s body, and the examiner asks the person a series of questions. The polygraph test measures the person’s physiological responses, such as rising blood pressure, to the questions to determine if they are telling the truth.

How can this lead to a wrong result? As one example, a person could be nervous and worry about the results of the test even if they are telling the truth, leading to higher blood pressure readings, and causing the machine to think they are lying.

Should You Take a Polygraph Test?

Although lie detector results are not always admissible in court, many attorneys and police officers continue to use the technology when questioning witnesses and suspects. If law enforcement administers a polygraph examination to a suspect, they also need to issue you your Miranda warning before conducting the test.

You should never agree to take a lie detector test without first consulting with a criminal defense lawyer if police want to question you about a crime. Your lawyer will help you think through what the results could mean for your case.

Talk to a Criminal Defense Lawyer Today

A criminal defense lawyer will give you legal advice and hold law enforcement agencies and prosecutors accountable. The attorney-client privilege will also let you tell your lawyer anything. Even if police cannot use the test results as evidence against you, they may use it in building a case. Just like you should always take advantage of your right to remain silent and right to an attorney, you can refuse to take this test.