Lie detectors, also known as polygraph machines, record a person’s physiological changes while they answer questions. They are commonly used in police interrogation and are sometimes required for certain government jobs.

A polygraph test records a person’s heart rate, blood pressure, respiration and sweat gland activity. Lying can cause all of these to rise, and the machine interprets these signals as signs of deception.

Blood Pressure

Most psychologists agree that the polygraph — or “lie detector” — is more a myth than a scientifically valid device for detecting deception. While the image of a polygraph pen wildly gyrating on a chart has become a cultural icon in crime dramas and movies, it’s based on a false assumption that liars have different physiological responses than truth tellers.

Hypertension, for example, can affect blood pressure and heart rate readings on a polygraph test. Medications taken for this condition can also lower the baseline for these measurements, so that an examiner could mistakenly interpret an increase as a sign of lying.

Coughing, sneezing or being sick during a lie detector test may also affect a person’s blood pressure and heart rate. The best way to beat a polygraph test is to remain completely still from start to finish. The Internet is full of advice for beating polygraph tests, but biting your tongue or putting a tack in your shoe won’t make you sweat any less and probably won’t fool the examiner.


A polygraph, or lie detector, displays a subject’s physiological responses as they answer questions. It is widely used in a variety of contexts, including interrogation and employment screening. Polygraphists rely on the assumption that people who are lying will exhibit certain physical reactions, such as a racing heartbeat and increased blood pressure.

When an examinee answers a question that is relevant to the crime or issue under investigation, the polygraph will record their response. The examiner will then ask a series of control questions. The examiner will analyze the data and determine whether there are any irregularities that may indicate deception.For more info, do visit this website Lie Detector Test.

Lombroso, a criminologist, discovered in the late nineteenth century that a person’s blood pressure and pulse rate increase when they tell lies. His findings led to the development of the first lie detection machine in 1921, which simultaneously traced a person’s blood pressure and respiration. However, these changes are easily influenced by factors that are not related to deception, such as stress and anxiety.

Galvanic Skin Response

The skin is the largest organ in the human body and is a primary interface between the external environment and the internal body. It enables us to perceive and respond to physical or emotional stimuli that affect the autonomic nervous system, which controls bodily functions like heart rate, breathing, and digestion.

GSR, also known as electrodermal activity or skin conductance response, measures changes in the skin’s electrical properties resulting from physiological arousal. When external or internal stimulation occurs that is arousing, the sympathetic nervous system activates sweat glands in the hands and feet which causes the skin to become a better conductor of electricity resulting in a measurable change in GSR.

During a polygraph test, the examiner will attach sensors to the wrists and knuckles to measure blood pressure, respiratory effort, and GSR. He will then ask neutral questions to establish a baseline measurement, and then intersperse relevant and control questions and record your responses. The computer will then analyze your answers to determine whether you are lying by comparing them to your baseline reading.

Electrodermal Activity

Originally, polygraphs were simply medical devices that recorded physiological changes. A trained examiner would hook the subject up to sensors like a blood pressure cuff, two pneumograph tubes strapped to the chest and abdomen, and electrodes on their fingers for galvanic skin response and breathing measurement. He would then intersperse control questions (vaguely threatening ones that aren’t relevant to the case at hand, like “Have you ever stolen anything?”) with relevant questions.

The results are displayed on a computer monitor for interpretation by the examiner. The underlying theory is that lying causes anxiety, which in turn leads to the physical responses mentioned above.

The entire procedure typically takes a few hours. During this time, you will be asked to answer several sets of questions and may be given short breaks between each session. People with certain health problems, such as epilepsy, heart disease, or mental illness, shouldn’t take the test. They may also be excluded if they’re taking certain medications or are pregnant.