What is a Polygraph or Lie Detector Test?

A polygraph test, also known as a "lie detector test," is not something out of the movies anymore. Polygraphs are a common part of criminal investigations and background checks. More and more companies, especially government bodies, now require a polygraph test from potential employees.

A polygraph test is a simple machine that consists of six sensors or "wires" that are attached to the person taking the test. The examiner, known as forensic psychophysiologist (FP), observes a sheet of moving paper and the type of lines drawn on it by a special pen. These lines vary according to the emotional reaction of the person to the questions, and these signals are recorded on paper.

Despite what the name suggests, a polygraph test does not detect lies, but rather evaluates the physical responses of a person to a series of questions. To do that, a polygraph test evaluates a person's heart rate, breathing rate, blood pressure, and perspiration on fingertips. Sometimes, a polygraph test also evaluates involuntary arm and leg movements and nervous tics, which are often found during difficult questions. Generally, when a person lies, his or her heart rate increases, he starts sweating, and his whole body reacts. This is what a polygraph test measures.