The polygraph, or the lie detector as it is often referred to, measures autonomic nervous system activity by sensors attached to different parts of the body. The sensors measure changes in breathing, cardiac activity and sweating. The indicators only show physiological changes, usually induced by emotion. The machine amplifies signals picked up from sensors placed at specific parts of the body. It detects not lies, but physical changes that are the results of specific emotions. People are asked ‘hot’ or relevant questions as well as ‘cool’ or control questions. The assumption is that for innocent people there is no physical difference in the way they respond to relevant and control questions. The other assumption is that suspect can be identified if he or she exhibits physical changes in his or her body. Therefore, suspects who are to be tested by polygraph use certain drugs to suppress autonomic nervous system activity and make any physiological recording inconclusive. More worryingly, people can be trained to defeat the test with a range of techniques. Tests would therefore not only be highly unreliable but counterproductive: alienating and misclassifying the innocent and letting the guilty get away without receiving the punishment he or she deserves.