A lie detector is definitely an instrument uses to detect blood pressure, respiration and pulse.

This instrument usually uses as being a forensic instrument. It is commonly used in police station for investigation but this easy instrument may be use in your own home. A lie detector or polygraph machine is used to aid someone in finding out if someone is truthfully answering a specific set of questions. This is a combination of various devices employed to measure a person's physical responses as to what are known as control, relevant and irrelevant questions.