A polygraph, often referred to as a lie detector, measures and records blood pressure, pulse, respiration and skin conductivity, these sensors sits around the chest, arm and finger while the person is being questioned, the goal is to see if a person is telling the truth or lying.
A polygraph detects lies by these physiological changes. In some countries polygraph is used as an interrogation tool for suspects or to screen new employees. US Law enforcement, federal government and many police departments use it. In Canada they are allowed for investigation purposes but not for court evidence. In India is it legal if the defendant requests one. In Europe, varying from country to country, polygraphs are not considered as reliable evidence. It is also seen in Europe as validating, the right to remain silent.
The polygraph (lie detector) machine was invented by John Augustus Larson, a police officer in California and was the first police officer to have an academic doctorate and to use a polygraph in a criminal investigation. Co-inventor, Leonarde Keeler worked on producing the modern polygraph and was first used in 1937.
Many might be wondering how accurate a lie detector test is, which is understandable, since it has been controversial for so long. The problem is that there’s no evidence that any pattern of reactions points to a lie, because a person who is telling the truth could still be nervous and a dishonest person could be calm. A lie detector test is not perfect and can be fooled. By experts and critics a lie detector would be about 70-90 procent accurate. To take a lie detector test by a professional would cost around 200-2,000 dollar depending on the length of the test. You can also buy a polygraph machine that measures all the signs, but that would cost over 10,000 dollar.