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Are Lie Detector Tests Admissible?

Lie detector tests, also called polygraphs, are a tool police use as part of their investigation. A suspect answers questions while hooked up to the lie detector. Based on certain readings, the polygraph examiner will conclude whether the person told the truth or lied.

Polygraph tests are controversial. For one thing, they are not 100% foolproof. Plenty of people “fail” a polygraph when they were really telling the truth, and some people pass even though they are lying through their teeth.

The good news is that polygraph results are very rarely admissible in criminal court. What’s more, you do not have to take one and, in fact, should decline. Our Houston criminal defense attorney explains below.

What is a Lie Detector?

A lie detector is a machine which measures certain physiological changes, such as heart rate, blood pressure, and respiration. The person taking the test is hooked up via electrodes and asked a series of “yes or no” questions. Based on the physiological response, the examiner attempts to gauge whether the person is lying or telling the truth when they answered.

For example, if someone’s heart rate spikes when answering, the assumption is that they are lying. By contrast, if they have an even heart rate and blood pressure, then the assumption is that they are answering a question truthfully.

Polygraph tests are not scientifically reliable. In fact, they are vulnerable to both false positive and false negative results.

Can the State Introduce Polygraph Results?

No, with very limited exceptions. The state can’t use polygraph results which allegedly show you were lying and submit them to a jury as proof.

Why Do Police Use Polygraph Exams?

Some police use them as part of an investigation. For example, witnesses might disagree about whether you were participating in a crime. A polygraph could clear up some confusion and help the police decide whether to identify you as a primary suspect.

Other officers use them to put pressure on a suspect to confess. Some people might break down from the stress and admit to participating in the crime, especially if confronted with a “failed” test result.

Should You Take a Polygraph Test?

Absolutely not. Furthermore, you have no obligation to take one, and the state can’t force you. All suspects have a Constitutional right to remain silent, and we recommend that you immediately exercise that right at the police station.

What if You Are Innocent?

You still shouldn’t take one. Although the police can’t introduce the results of a polygraph, they might use anything you say during the exam against you. Who knows what you might say that could sound incriminating to the police? Again, silence is the best policy if you are a suspect.

Contact a Houston Criminal Defense Attorney

Being hauled into the police station is a disorientating experience. Many people just want to go home and willingly answer police questions because they think they’ll be released quicker. Instead of agreeing to an interrogation, please contact Tad Nelson today. Our law firm can jump in and defend your freedom.