The polygraph is a complex device with several components governing its action. If you’re scheduled for a lie detector test, understanding how the polygraph works can help you relieve pre-exam stress and anxiety you feel towards the process.

By understanding more about the polygraph, you remove the fear of the unknown, helping you eliminate pre-exam jitters. This post discusses the four key components of the polygraph. We’ll also look at other device elements used to detect deception in examinees.


A Brief History of the Development of the Polygraph

The history of the polygraph starts in the late 1800s. Several men contributed to the field around this time, but the most important innovation came from Dr. James MacKenzie. As a cardiologist, MacKenzie had a keen understanding of the heart and lungs and how they affected physiology.

In an attempt to detect heart disease in an early stage, MacKenzie developed his “polygraph” device, debuting it in 1902. He was the first to coin the expression, but ironically, his machine was not used in deception detection practices. It was built specifically for medical use.

Across the pond in the United States, psychologist and law student William Marston developed his “Systolic Blood Pressure Test” after becoming intrigued with the effects of the “fight-or-flight” response on the cardiovascular system. His device measured changes in blood pressure during questioning processes to determine if the examinee was acting deceptively with their answers.

Marston’s work inspired John A. Larson, who would make the first breakthrough in real polygraph science. Larson, a Ph.D., spent time during his university studies moonlighting with the Berkeley Police Department. He developed the “Sphyggy,” the world’s first lie detector in law enforcement interrogations.

During Larson’s time with the Berkeley Police Department, he met Leonard Keeler. Keeler advanced Larson’s original design, making it more effective and user-friendly, naming his innovation “The Emotograph.” After losing the device in a fire at his department in 1925, Keeler teamed up with a Chicago firm, “Associated Research,” to redevelop and redesign his Emotograph.

Keeler passed away in 1949, but Associated Research kept developing new versions of his polygraph. Around this time, other companies, such as Stoelting, started releasing polygraph machines, and the industry of polygraphy took off.

These electro-mechanical/analog devices were in use until the 1990s, when Axciton Systems, in collaboration with John Hopkin Laboratory, developed the first software-driven polygraphs. This brings us to the modern age of computerized polygraph systems.


What are the Four Components of a Lie Detector Test?

The lie detector machine consists of four primary components to monitor the examinee’s physiological response to questioning. Let’s look at each of them in detail.



This instrumentation involves two 10-inches convoluted corrugated rubber tubes secured to the examinee’s abdomen and chest. The tubes expand and contract as the examinee breathes, sending the respiration data to the software module.



This apparatus consists of a blood pressure cuff, pump, and the “sphygmomanometer.” It’s the same instrument the doctor uses when you visit their office and has them take your blood pressure. The cuff secures to the upper right arm, just above the fold in the elbow on the brachial artery.

When the cuff inflates, the contraction and distension of the muscle caused by the examinee’s blood pressure cause an increase in the internal pressure of the cuff and its bellows. The cuff sends data n changes in blood pressure and pulse rate to the software program on the examiner’s laptop.



This component consists of electrodes attached to the examinee’s ring and index fingers on the left hand. Some devices have this component attached to the dorsal and palmar surface of the left hand. The galvanograph records the examinee’s electrical skin resistance.



This motor pulls or drives the chart paper on older Keeler and Stoelting polygraph models. These devices use pens to record the physiological changes in the examinee’s respiration rate, blood pressure, pulse, and skin electrical activity. Today’s modern polygraphs are software-driven, so they no longer use this component.


Other Components of Polygraph Devices in the Modern Era

The introduction of software-driven systems and innovations in polygraph science brought additional components to the technology. Today’s polygraphs feature elements that track the examinee’s sweat gland production; some may also track blood oxygenation.

Furthermore, some machines allow for the connection of a pressure mat the examinee sits on during the test. The pad records any movement the examinee makes during the exam.


The Role of Polygraph Software

The introduction of software to polygraph technology in the early 1990s revolutionized the industry. Before this date, the examiner would look at chart paper on the device, with the pens creating oscillating lines when interpreting the examinee’s physiological feedback to questions.

The software did away with the need for chart paper and pens, replacing them with a PC or laptop screen. The instrumentation attached to the examinee feeds into a control box which plugs into the computer, allowing the software to interpret the examinee’s physiological data.

The introduction of software also allows for easier recording and storage of exam data instead of relying on chart paper and outdated filing systems. The examiner can play back the recording and re-examine the subject’s responses, comparing them to a video recording of the session.


What Triggers Changes in Our Physiology During a Polygraph Exam?

The purpose of the polygraph is to record changes in the examinee’s blood pressure, heart rate, respiration, sweat gland activity, and electrical skin activity under questioning. These vital signs change when we lie during the polygraph exam due to the activation of the “Fight-or-Flight” (FoF) response.


What Governs the “Fight-or-Flight” Response?

The FoF is a part of our evolution dating back to our hunter-gather ancestor’s tens of thousands of years ago. We didn’t live in civilized cities or towns during this time but as nomadic tribes. We would send out small groups of people on hunting trips to find sustenance in the wild.

During these adventures, we would encounter large predators, such as big cats. If they caught us, we were their dinner. So, we developed the FoF to help us escape or ward off these wild animals, allowing us to survive.

The brain interprets electrical signals from the Central Nervous System (CNS) and the Peripheral nervous system (PNS). The PNS governs the function of the Autonomic Nervous system, which activates the Parasympathetic Nervous System (PSNS) and the Sympathetic Nervous System (SNS).

When we feel stressed, such as spotting a big cat stalking us on the plains of Africa, the SNS primes the FoF. You’ll notice this yourself in scenarios where you feel scared, such as watching a horror movie. You get goosebumps, and the hairs on your neck stand on end. You start to sweat a little, and your pupils widen to allow more light to enter your eyes and sharpen your vision.

Your heart starts racing, and you feel on edge – that’s the FoF working on your physiology to get you to think about running away from what it perceives as a threat or to stand and face it. When the danger subsides, those physiological markers all return to the resting baseline, and life goes on – hopefully.

However, in the modern world, we don’t have big cats stalking us anymore. However, the FoF is ingrained in our physiology. As a result, it activates for different reasons. We all experience stress from time to time in our lives.

In this regard, the polygraph presents a threat to our livelihood and well-being. We don’t know what to expect from it, so stress builds in our minds and nervous system. As the date of your polygraph[h exam nears, the SNS starts to prepare you for the pending risk ahead.

It primes the FoF, preparing it for launch when the right stimulus appears in your environment. In this case, the catalyst that triggers the FoF response is when the polygraph examiner asks you a question, and you have to lie to protect yourself. Immediately, you feel a jolt of energy rock your body as the FoF activates.


How Does the Examiner Determine Deception in an Examinee?

The examiner and the polygraph are looking for signs of the FoF response as they question you during the exam. They understand its impact on our physiology, and the specialized components of the polygraph track your physiological reaction as the exam progresses.

When you lie, you activate the FoF, and the polygraph picks up these changes in your body. The examiner will see these changes in the charts they watch on their computer screen. If they notice the activation of the FoF, they’ll repeat the question triggering the response.

If you continue to react in a manner that triggers the FoF, they’ll stop the exam and ask you why they’re getting a reading that you’re acting deceptively. If you don’t have an explanation, it confirms that what they see is deceptive behavior.


How Accurate Is the Polygraph?

In the days of the Keeler polygraph, experts thought the device was anywhere from 50% to 70% accurate at detecting deception in examinees. While that’s impressive, it cast doubt on the validity of polygraph results, as there was a potential for the device to register false positives during the exam.

However, the integration of software into the technology improved test accuracy. Experts in polygraph science state the modern device is up to 97% accurate at detecting deception. Despite the improvements in polygraph technology in the last three decades, many people still view polygraph as inaccurate due to its past reputation.

As a result, the courts and justice system still implement the rules surrounding polygraph results as admissible evidence in criminal trials. It’s also why the “Employee Polygraph Protection Act of 1988” (EPPA) is still in place.


Can I Beat the Polygraph?

During the 1950s, people discovered that implementing “countermeasures” during polygraph exams could interfere with the device’s accuracy. A countermeasure is a tactic the examinee uses before or during the test to intentionally interrupt the body’s launch of the FoF, thereby influencing the device’s interpretation of their physiological feedback.

There are three types of countermeasures.


Informational & Psychological Countermeasures

These countermeasures involve researching how to beat the polygraph test. They also include tactics like thinking bad thoughts when the examiner asks a question to interrupt the activation of the FoF.

Physical Countermeasures

These countermeasures involve clenching your leg muscle or biting your tongue when the examiner asks a question.

Drug-Based Countermeasures

Medications like benzodiazepines (Xanax) are a modern touch on countermeasures. These drugs lower anxiety in the body, dampening the FoF mechanism. However, they can’t completely eliminate the stress of the exam, and the examiner is likely to discover your use of these medications.


The issue with countermeasures is that most of them come from the “Keeler” polygraph era. While these strategies might have had some effect on the older devices, the new software-driven systems used in exams today can tell if the examinee is using these tactics in an attempt to influence the outcome of the test.

Examiners have specialized training to help them interpret when an examinee might be using countermeasures during the lie detector test. So, suppose you research any countermeasures and decide to use them in the exam. In that case, there’s a good chance the examiner will figure it out, and you’ll fail the polygraph exam.


What Is the Future of Polygraph Science?

Polygraph science is progressing at an accelerated rate, especially as we move into the Artificial Intelligence (AI) era. An AI-based polygraph system is already in play worldwide, especially in government operations.

For instance, the US, Canada, and EU have an AI-baaed polygraph called “AVATAR,” which they use to screen immigrants for possible terror threats. The AI is remarkably accurate, with success rates of between 60% to 80% in determining if the immigrant is being deceptive.

At the moment, these systems don’t act independently. If they determine the examinee is acting deceptively, they refer them to a human-led test for further investigation. However, it’s clear that polygraph technology is moving in this direction. It won’t be long before we see fully-autonomous AI polygraph technology come to light.