How Does A Lie Detector Test (a.k.a. Polygraph) Work?

You hear about lie detector tests a lot in police or criminal investigations, and sometimes a person applying for a position in the law enforcement (FBI or CIA). The aim of a lie detector is to check if the person is lying or telling the truth while answering to a set of questions.

When a person takes a lie detector test, a machine with four to six sensors will be attached to him. This machine will record the multiple ("poly") signals from the sensors and have it reflect on a single strip of moving paper ("graph").

A polygraph machine is an instrument which is basically a mixture of medical devices able to monitor inconsistencies or changes occurring in the body. While the person is questioned about a particular event or incident, the examiner will check the person's blood pressure, respiratory rate, heart rate, and electrodermal activity such as perspiration of the face or fingers, and record any sudden change in comparison to the person's normal levels. Why? Because these fluctuations serve as indications that the person is being deceitful, but examination results will still open to evaluation by the examiner. Visit us at for more details.

Lie detector tests are usually associated with criminal investigations. However, there are other cases in which they can be found very useful. You may one day encounter a lie detector test just before being hired for a job. As many government agencies, and some big private-sector companies, will make it a requirement that you undergo a polygraph examination before they proceed with the employment.

Lie detector tests are designed to look for substantial involuntary responses going on in a person's body when he's made to go through stress, such as the stress linked to deception. Check us out at for additional information.

For a very long time now, a lot of experts - such as psychologists, scientists, actual examiners and even the manufacturers of the machine - argue that the lie detector test cannot specifically, and accurately, detect if a person is lying. Studies even show that the accuracy rate of lie detector tests is only at 85% (National Academy of Sciences, 2003). But it's proven that there are very distinct physiological responses that most of us go through when we make an attempt to deceive another person. So by asking questions about a particular issue being investigated, and by monitoring a subject's physiological responses to those questions, a polygraph examiner can objectively determine if deceptive behavior is being demonstrated. This is the closest we can get to finding out if a person is being genuine or not. You can also learn more about lie detectors by checking out the post at .