Polygraph tests -- also called "lie detectors" -- have been around so long that they're a permanent part of the way American's picture law enforcement operations. In the movies and on television, the police can hook a suspect up to a polygraph machine and make a clean call about their guilt after just a few questions.
Well, it really doesn't work that way. Psychologists say that the machine is better described as a "fear detector," than any kind of lie detector. To detect a "lie," the polygraph machine measures such things as a suspect's:
- Rises in blood pressure
- Changes in breathing
- A quickening heart rate
- Increased sweating
While all of these physiological changes could occur when someone is lying, they could just as easily occur when someone is scared. (Keep in mind that you don't have to be guilty of anything to be terrified when you're sitting in a police interrogation room strapped to some wires while under the clear impression that your future depends on what a machine says about your truthfulness.)
In addition to not being able to credibly tell ordinary anxiety and fearfulness over the situation from a lie, there's every possibility that the people polygraphs are designed to detect can easily fool the machine if they try. Strategies that are widely shared via the internet showing people how to "beat the machine" seem to be effective. Anyone who plans on lying during the test is much more likely to investigate these kinds of strategies than someone who is telling the truth.
Polygraphs have long been banned from federal courts as evidence because they aren't deemed reliable. Don't allow investigators to use pseudo-science like a polygraph to intimidate you or push you into a confession by making you believe that the evidence they have is irrefutable. Contact a defense attorney to learn more about your legal rights.