A popular way in many crime films to determine whether a suspect is lying or telling the truth is to hook him up to a polygraph machine. Within a minute the police can determine whether the suspect is lying and guilty or, on rare occasions, telling the truth and innocent. But you have to ask yourself: is it really that simple? Polygraphs measure four main factors that are believed to change when a lie is told, and most importantly, these changes are assumed to indicate deception. The four main factors are blood pressure, heart rate, sweating and breathing and these are recorded using simple devices. It is important to note from the outset that those who question the reliability of polygraphs are not doubting the reliability of the measurements, but the ability of the measurements to indicate and/or demonstrate deception. While there are questions about reliability, polygraphs are used not only in law enforcement, but also in intelligence agencies, in maintaining the security of industry, and for public safety and service around the world. Despite its prevalence, there are many groups that question the effectiveness, reliability, and fairness of polygraph tests. This article will explore this question by first examining the history of polygraphs, including court rulings and how polygraph tests are performed, then current use, and finally examining the sources of bias and error in the test and trial. Means of lie detection were used. long before the modern polygraph was invented. For example, in the 18th century, a person's hand was placed in a pot filled with boiling water and if his hand burned, then he was believed to be lying (The History and Basic Facts of Polygraph, 2009). At the end... half of the paper... the question") with your answer to a question regarding the issue under investigation” (a relevant question) (Polygraph FAQ, 2006). “If the reactions to the question of " control" are greater, the subject is judged to be truthful. If the reactions to the question on which the polygraph is attempting to determine truth or deception are greater, the subject fails. If the reactions to both are approximately the same size, the test is defined as inconclusive.” (Polygraph FAQ, 2006). Works CitedPolygraph FAQ (2006). /polygraphexaminer.com/polygraph-history.htmlPolygraph Laws of Admissibility (2011 Retrieved from ThePolygraphExaminer.com: http://www.thepolygraphexaminer.com/polygraph_laws.htm).