A polygraph, more commonly known as a lie detector, is a test used in criminal investigations that measures physiological responses in a subject’s body as they answer a series of questions.
Despite what crime shows may lead viewers to believe, administering a lie detector test is not all that common. This is because only 18 states in the US allow them to be used in a trial. Arizona is among those states.
Lie Detector Tests in Arizona
Arizona will allow polygraph exams as evidence in a case. However, the state has an additional rule that they are not admissible, or valid, in court unless both the defense and the prosecution agree upon it. The judge in the trial also has the power to decide whether to allow the test or not.
Lie detector tests can also be used as part of a screening protocol for high-security jobs, like CIA and FBI agents. This is described in Arizona Revised Statutes (ARS) 38-1108, which details the polygraph examination exceptions.
How Lie Detector Tests Work
A polygraph is used to help determine whether or not someone is telling the truth. They do not directly measure deception, however, but rather possible signs of it. The test does so by recording different bodily responses to a series of questions, including increased blood pressure, heart rate, breathing, and sweating.
The person administering the test starts by asking straightforward, control questions to relax the interviewee. These questions are designed to require mainly yes or no answers.
Next, the subject is hooked up to the equipment, which consists of four to six sensors (hence the name “poly”). This typically includes a blood pressure monitor on one finger, a cuff on another to detect skin conductivity, and tubes wrapped around the chest and stomach to monitor breathing.
As the test administrator asks the relevant questions, they will observe graphs of the subject’s vital signs. Spikes in these vitals will usually indicate to them that their subject is trying to be deceitful.
How Accurate is a Lie Detector Test?
Lie detectors are not always accurate. They are estimated to be correct between 75% and 87% of the time, but results depend on a variety of factors. These include the equipment used to administer the test, how the questions are formulated, and misinterpretation of the results.
Even if they are telling the truth, innocent people may fail a polygraph test simply because they are nervous to take it. Feeling anxious can raise blood pressure, which is one sign of deception according to the test. In addition, passing the test does not ensure that you won’t still be charged with the crime in question.
Know Your Rights Surrounding a Lie Detector Test
You are under no legal obligation to take a lie detector test without consulting an attorney first. Also, a law enforcement officer must read you your Miranda rights before issuing the test. You can exercise your right to remain silent and your right to an attorney before taking it.
Speak With a Criminal Defense Lawyer in Tucson
If you have been asked to take a polygraph by an officer, the DUI Defense Team can discuss your options with you. Our attorneys specialize in criminal and assault defense, domestic violence, and DUIs.
