How do Lie detectors work?

A lie detector works on the principle that a person who tells a lie is nervous and under stress. Under these conditions his body undergoes some physiological changes.

These include increases in the blood pressure, heart beat rate and perspiration on hands and soles. These changes are monitored and detected by a lie-detector. The person to be examined is made to wear a chest band, a blood pressure cuff and electrodes on his palms.

He is then subjected to a series of questions in order to see his normal reactions.

This is followed by more probing questions. Based on his responses a trained specialist can find out whether the accused person.