Lies are part of human life! People often tell lies to deceive others. many of us have heard about “lie detector “,some where seen in movies or read it in fiction stories. Does anything of this sort really exist? If yes, does it really detect lies? Yes it does. The first thing that comes to our mind is how an instrument with some electronic components can read out our mind. Though science and technology are growing at the speed of light, has it reached a stage where it can read mind? Not exactly! But it can approach to that stage by monitoring the physiological reaction by plotting graphs. When someone decieves, sometimes we are able to guess by his/her reactions whether they are deceiving or not. But most of the times we are unable to predict this. This principle of guessing is more widely used with the growing technologies to monitor the physiological reactions. It monitors the involuntary change that occurs in the body when the person is under stress. Biomedical instruments are used to monitor those physiological reactions.