The lie detector can only judge whether a small number of people are lying, because these people are prone to blush and heartbeat when lying, which will lead to obvious abnormal heart rate, and the lie detector will detect it. But for a liar, his face will not turn red and his heart will not accelerate. This lie detector is of little use. Because he has a strong chance when testing, real police stations and other institutions will not regard it as a machine to verify prisoners. Many people who don't lie also feel nervous when asked questions, so their judgment is very unstable.

First, the way to judge the lie detector

When judging whether a person is lying, people can judge from his body movements and eyes. In the case of lying, most people's body movements are unnatural, they will blush and even scratch their ears, and their eyes will become erratic. Polygraph is used to test people's breathing, pulse, skin resistance and other phenomena that are not easy to be found. People can tell whether this person is lying by changing the frequency.

Second, the instability of the polygraph.

Although people's breathing frequency, pulse and resistance may be the basis for a person to lie. But in some people who don't lie, there will be obvious fluctuations when they are asked questions, which is caused by nervousness. For those with good psychological quality, they will not be nervous even if they are questioned by the police. On the contrary, these people may not find any fluctuation in the polygraph test. Because of the existence of such people, the lie detector has strong inaccuracy, so it is difficult to judge whether it is true or false.

When judging whether a person is lying, the other person's deliberate disguise will also affect your judgment. The lie detector is not a universal tool, and its accuracy is related to the use environment.