Lie detector is a device which is capable of detecting a person telling lie. In 1921 John A Larson, a medical student of California University, USA made a device that could detect lies with a lot of ‘Polygraph’ or lie detector. American inventor Allan Bell prepared another improved model of a lie detector in 1972. His lie detector was capable of detecting slight trembling in the voice which mostly occur when a person tells a lie. Today the lie detector is greatly used in crime detection.
How does the machine lie detector detect lies is very interesting. When someone tells a lie, some particular physiological changes occurs in his body. His heart starts beating faster leading to rapid perspiration. His blood pressure and breathing pattern also alter. Again his voice begins trembling. The lie detector machine is designed to record all these changes.
When a person undergoes a lie-detector test, different parts of the machine are attached to his body by wires. The expert taking the test called the interrogator asks the person questions about all relevant things. The physiological changes going on during questioning are appeared on the computer screen and are recorded by a pen recorder fitted in the instrument. At last these observations are studied. His general conversation before the test and his reaction during the test are compared. From his recorded behaviour and physiological changes it is proved that whether he is telling lie or not.
However, the lie-detecting or polygraphy is not entirely dependable. Its accuracy is said to be around 80%. Much depends upon the skill of the examiner conducting the test. The people who are unaware of the fact that they are telling lie, they can not be caught by the detector. Again, the intelligent and hardened criminals can manage their emotions and render this machine futile. Because of these reasons the readings of a lie-detector test can not be accepted as evidence in the court of law. However, it is being used by the police departments in most countries of the world. What they are benefited from it is that, by this test they get the clues to catch the criminals.