A polygraph, popularly referred to as a lie detector, measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions. The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers.
The polygraph was invented in 1921 by John Augustus Larson, a medical student at the University of California, Berkeley and a police officer of the Berkeley Police Department in Berkeley, California.  The polygraph was on the Encyclopædia Britannica 2003 list of greatest inventions, described as inventions that "have had profound effects on human life for better or worse." 
The efficacy of polygraphs is debated in the scientific community. In 1991, two thirds of the scientific community who have the requisite background to evaluate polygraph procedures considered polygraphy to be pseudoscience. In 2002, a review by the National Research Council found that, in populations "untrained in countermeasures, specific-incident polygraph tests can discriminate lying from truth telling at rates well above chance, though well below perfection". The review also warns against generalization from these findings to justify the use of polygraphs—"polygraph accuracy for screening purposes is almost certainly lower than what can be achieved by specific-incident polygraph tests in the field"—and notes some examinees may be able to take countermeasures to produce deceptive results. 
In some countries, polygraphs are used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. US law enforcement and federal government agencies such as the FBI, NSA  and the CIA and many police departments such as the LAPD use polygraph examinations to interrogate suspects and screen new employees. Within the US federal government, a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination.
Polygraph testing is designed to analyze the physiological reactions of subjects. However, research has indicated that there is no specific physiological reaction associated with lying and that the brain activity and mechanisms associated with lying are unknown, making it difficult to identify factors that separate liars from truth tellers. Polygraph examiners also prefer to use their own individual scoring method, as opposed to computerized techniques, as they may more easily defend their own evaluations.
The validity of polygraph testing is again called into question with the relevant-irrelevant testing technique, designed to gauge reactions of subjects against crime questions and other non-crime related questions. Studies have indicated that this questioning technique is not ideal, as many innocent subjects exert a heightened physiological reaction to the crime relevant questions.
The control question test, also known as the probable lie test, was developed to combat the issues with the relevant-irrelevant testing method. Although the relevant questions in the probable lie test are used to obtain a reaction from liars, the physiological reactions that "distinguish" liars may also occur in innocent individuals who fear a false detection or feel passionately that they did not commit the crime. Therefore, although a physiological reaction may be occurring, the reasoning behind the response may be different. Further examination of the probable lie test has indicated that it is biased against innocent subjects. Those who are unable to think of a lie related to the relevant question will automatically fail the test.
Polygraph examiners, or polygraphers, are licensed or regulated in some jurisdictions.  The American Polygraph Association sets standards for courses of training of polygraph operators, though it does not certify individual examiners. 
The examiner typically begins polygraph test sessions with a pre-test interview to gain some preliminary information which will later be used to develop diagnostic questions. Then the tester will explain how the polygraph is supposed to work, emphasizing that it can detect lies and that it is important to answer truthfully. Then a "stim test" is often conducted: the subject is asked to deliberately lie and then the tester reports that he was able to detect this lie. Guilty subjects are likely to become more anxious when they are reminded of the test's validity. However, there are risks of innocent subjects being equally or more anxious than the guilty. Then the actual test starts. Some of the questions asked are "irrelevant" ("Is your name Fred?"), others are "diagnostic" questions, and the remainder are the "relevant questions" that the tester is really interested in. The different types of questions alternate. The test is passed if the physiological responses to the diagnostic questions are larger than those during the relevant questions.
Criticisms have been given regarding the validity of the administration of the Control Question Technique. The CQT may be vulnerable to being conducted in an interrogation-like fashion. This kind of interrogation style would elicit a nervous response from innocent and guilty suspects alike. There are several other ways of administering the questions.
An alternative is the Guilty Knowledge Test (GKT), or the Concealed Information Test, which is used in Japan. The administration of this test is given to prevent potential errors that may arise from the questioning style. The test is usually conducted by a tester with no knowledge of the crime or circumstances in question. The administrator tests the participant on their knowledge of the crime that would not be known to an innocent person. For example: "Was the crime committed with a .45 or a 9 mm?" The questions are in multiple choice and the participant is rated on how they react to the correct answer. If they react strongly to the guilty information, then proponents of the test believe that it is likely that they know facts relevant to the case. This administration is considered more valid by supporters of the test because it contains many safeguards to avoid the risk of the administrator influencing the results.
Polygraphy is widely criticized.   Despite claims of 90% validity by polygraph advocates, the National Research Council has found no evidence of effectiveness.  The utility among sex offenders is also poor, with insufficient evidence to support accuracy or improved outcomes in this population.
Even using the high estimates of the polygraph's accuracy, false positives do occur, and these people suffer the consequences of "failing" the polygraph. In the 1998 US Supreme Court case United States v. Scheffer, the majority stated that "There is simply no consensus that polygraph evidence is reliable" and "Unlike other expert witnesses who testify about factual matters outside the jurors' knowledge, such as the analysis of fingerprints, ballistics, or DNA found at a crime scene, a polygraph expert can supply the jury only with another opinion." The Supreme Court summarized their findings by stating that the use of polygraph was "no more accurate than coin flip."  In 2005, the 11th Circuit Court of Appeals stated that "polygraphy did not enjoy general acceptance from the scientific community".  In 2001, William Iacono, Professor of Psychology and Neuroscience at the University of Minnesota, concluded that:
Although the CQT [Control Question Test] may be useful as an investigative aid and tool to induce confessions, it does not pass muster as a scientifically credible test. CQT theory is based on naive, implausible assumptions indicating (a) that it is biased against innocent individuals and (b) that it can be beaten simply by artificially augmenting responses to control questions. Although it is not possible to adequately assess the error rate of the CQT, both of these conclusions are supported by published research findings in the best social science journals (Honts et al., 1994; Horvath, 1977; Kleinmuntz & Szucko, 1984; Patrick & Iacono, 1991). Although defense attorneys often attempt to have the results of friendly CQTs admitted as evidence in court, there is no evidence supporting their validity and ample reason to doubt it. Members of scientific organizations who have the requisite background to evaluate the CQT are overwhelmingly skeptical of the claims made by polygraph proponents. 
Summarizing the consensus in psychological research, professor David W. Martin, PhD, from North Carolina State University, states that people have tried to use the polygraph for measuring human emotions, but there is simply no royal road to (measuring) human emotions.  Therefore, since one cannot reliably measure human emotions (especially when one has an interest in hiding his/her emotions), the idea of valid detection of truth or falsehood through measuring respiratory rate, blood volume, pulse rate and galvanic skin response is a mere pretense. Psychologists cannot ascertain what emotions one has,  with or without the use of polygraph.
Polygraphs measure arousal, which can be affected by anxiety, anxiety disorders such as posttraumatic stress disorder (PTSD), nervousness, fear, confusion, hypoglycemia, psychosis, depression, substance induced states (nicotine, stimulants), substance withdrawal state (alcohol withdrawal) or other emotions; polygraphs do not measure "lies".   A polygraph cannot differentiate anxiety caused by dishonesty and anxiety caused by something else. 
The polygraph is inherently subjective.  It relies heavily on interpretation by the examiner, so human error (which could be caused by examiner inexperience) and bias can result in the examiner drawing the wrong conclusion. 
US Congress Office of Technology Assessment
In 1983, the US Congress Office of Technology Assessment published a review of the technology  and found:
...there is at present only limited scientific evidence for establishing the validity of polygraph testing. Even where the evidence seems to indicate that polygraph testing detects deceptive subjects better than chance, significant error rates are possible, and examiner and examinee differences and the use of countermeasures may further affect validity. 
National Academy of Sciences
The accuracy of the polygraph has been contested almost since the introduction of the device. In 2003, the National Academy of Sciences (NAS) issued a report entitled "The Polygraph and Lie Detection". The NAS found that the majority of polygraph research was "unreliable, unscientific and biased", concluding that 57 of the approximately 80 research studies that the American Polygraph Association relies on to come to their conclusions were significantly flawed.  These studies did show that specific-incident polygraph testing, in a person untrained in counter-measures, could discern the truth at "a level greater than chance, yet short of perfection". However, due to several flaws, the levels of accuracy shown in these studies "are almost certainly higher than actual polygraph accuracy of specific-incident testing in the field". 
When polygraphs are used as a screening tool (in national security matters and for law enforcement agencies for example) the level of accuracy drops to such a level that "Its accuracy in distinguishing actual or potential security violators from innocent test takers is insufficient to justify reliance on its use in employee security screening in federal agencies." The NAS concluded that the polygraph "...may have some utility"  but that there is "little basis for the expectation that a polygraph test could have extremely high accuracy". 
The NAS conclusions paralleled those of the earlier United States Congress Office of Technology Assessment report "Scientific Validity of Polygraph Testing: A Research Review and Evaluation".  Similarly, a report to Congress by the Moynihan Commission on Government Secrecy  on national security concluded that "The few Government-sponsored scientific research reports on polygraph validity (as opposed to its utility), especially those focusing on the screening of applicants for employment, indicate that the polygraph is neither scientifically valid nor especially effective beyond its ability to generate admissions...".
Several countermeasures designed to pass polygraph tests have been described. Asked how he passed the polygraph test, Aldrich Ames explained that he sought advice from his Soviet handler and received the simple instruction to: "Get a good night's sleep, and rest, and go into the test rested and relaxed. Be nice to the polygraph examiner, develop a rapport, and be cooperative and try to maintain your calm". Additionally, Ames explained, "There's no special magic....Confidence is what does it. Confidence and a friendly relationship with the examiner...rapport, where you smile and you make him think that you like him". 
Other suggestions for countermeasures include for the subject to mentally record the control and relevant questions as the examiner reviews them before the interrogation begins. During the interrogation the subject is supposed to carefully control their breathing while answering the relevant questions, and to try to artificially increase their heart rate during the control questions, for example by thinking of something scary or exciting, or by pricking themselves with a pointed object concealed somewhere on their body. In this way the results will not show a significant reaction to any of the relevant questions. 
There are two types of countermeasures: General State (intending to alter the physiological or psychological state of the examinee for the length of the test), and Specific Point (intending to alter the physiological or psychological state of the examinee at specific periods during the examination, either to increase or decrease responses during critical examination periods). 
Law enforcement agencies and intelligence agencies in the United States are by far the biggest users of polygraph technology. In the United States alone most federal law enforcement agencies either employ their own polygraph examiners or use the services of examiners employed in other agencies.  In 1978 Richard Helms, the 8th Director of Central Intelligence, stated that:
- "We discovered there were some Eastern Europeans who could defeat the polygraph at any time. Americans are not very good at it, because we are raised to tell the truth and when we lie it is easy to tell we are lying. But we find a lot of Europeans and Asiatics can handle that polygraph without a blip, and you know they are lying and you have evidence that they are lying." 
In Canada, the 1987 decision of R v Béland, the Supreme Court of Canada rejected the use of polygraph results as evidence in court. This decision did not, however, affect the use of the polygraph in criminal investigations. The polygraph is regularly used as a forensic tool in the investigation of criminal acts and sometimes employed in the screening of employees for government organizations.
In the province of Ontario, the use of polygraphs is not permitted by an employer. A police force does have the authorization to use a polygraph in the course of the investigation of an offence. 
In 2007, polygraph testimony was admitted by stipulation in 19 states, and was subject to the discretion of the trial judge in federal court. The use of polygraph in court testimony remains controversial, although it is used extensively in post-conviction supervision, particularly of sex offenders. In Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), the old Frye standard was lifted and all forensic evidence, including polygraph, had to meet the new Daubert standard in which "underlying reasoning or methodology is scientifically valid and properly can be applied to the facts at issue." While polygraph tests are commonly used in police investigations in the US, no defendant or witness can be forced to undergo the test. In United States v. Scheffer (1998), the US Supreme Court left it up to individual jurisdictions whether polygraph results could be admitted as evidence in court cases. Nevertheless, it is used extensively by prosecutors, defense attorneys, and law enforcement agencies. In the states of Massachusetts, Maryland, New Jersey, Oregon, Delaware and Iowa it is illegal for any employer to order a polygraph either as conditions to gain employment, or if an employee has been suspected of wrongdoing. The Employee Polygraph Protection Act of 1988 (EPPA) generally prevents employers from using lie detector tests, either for pre-employment screening or during the course of employment, with certain exemptions.  As of 2013, about 70,000 job applicants are polygraphed by the federal government on an annual basis.  In the United States, the State of New Mexico admits polygraph testing in front of juries under certain circumstances. In many other states, polygraph examiners are permitted to testify in front of judges in various types of hearings (Motion to Revoke Probation, Motion to Adjudicate Guilt).
In 2010 the NSA produced a video explaining its polygraph process.  The video, ten minutes long, is titled "The Truth About the Polygraph" and was posted to the website of the Defense Security Service. Jeff Stein of The Washington Post said that the video portrays "various applicants, or actors playing them – it’s not clear – describing everything bad they had heard about the test, the implication being that none of it is true."  AntiPolygraph.org argues that the NSA-produced video omits some information about the polygraph process; it produced a video responding to the NSA video.  George Maschke, the founder of the website, accused the NSA polygraph video of being " Orwellian ". 
In 2013, the US federal government had begun indicting individuals who stated that they were teaching methods on how to defeat a polygraph test.    During one of those investigations, upwards of 30 federal agencies were involved in investigations of almost 5000 people who had various degrees of contact with those being prosecuted or who had purchased books or DVDs on the topic of beating polygraph tests.   
In 2008, an Indian court adopted the Brain Electrical Oscillation Signature Profiling test as evidence to convict a woman, who was accused of murdering her fiancé. It is the first time that the result of polygraph was used as evidence in court.  On May 5, 2010, The Supreme Court of India declared use of narcoanalysis, brain mapping and polygraph tests on suspects as illegal and against the constitution if consent is not obtained and forced.  Article 20(3) of the Indian Constitution – "No person accused of any offence shall be compelled to be a witness against himself." Polygraph tests are still legal if the defendant requests one.
The Supreme Court of Israel, in Civil Appeal 551/89 (Menora Insurance Vs. Jacob Sdovnik), ruled that as the polygraph has not been recognized as a reliable device. In other decisions, polygraph results were ruled inadmissible in criminal trials. It has not been clearly decided if polygraph results are inadmissible as evidence in a civil trial.
In the private discipline, some insurance companies attempt to include a clause in insurance contracts, in which the beneficiary agrees that polygraph results be admissible as evidence. In such cases, where the beneficiary has willingly agreed to such a clause, signed the contract, and taken the test, the courts will honor the contract, and take the polygraph results into consideration. However, it is common practice for lawyers to advise people who signed such contracts to refuse to take the test. Depending on whether or not the beneficiary signed an agreements clause, and whether the test was already taken or not, such a refusal usually has no ill effects; at worst, the court will simply order the person to take the test as agreed. At best, the court will cancel the clause and release the person from taking the test, or rule the evidence inadmissible.
In most European jurisdictions, practice varies by country but polygraphs are generally not considered reliable evidence and are not generally used by law enforcement. Polygraph testing is widely seen in Europe to violate the right to remain silent.  :62ff
As of 2017 Belgium was the European country with the most prevalent use of polygraph testing by police, with about 300 polygraphs carried out each year in the course of police investigations. The results are not considered viable evidence in bench trials, but have been used in jury trials.  :62ff The polygraph was used in Lithuania for the first time in 1992. From the 2004 surveys on the use of the Ewent Knowledge Test (new version of the Concealed Information Test) for criminal investigation. 
The High Court of Australia has not yet considered the admissibility of polygraph evidence. However, the New South Wales District Court rejected the use of the device in a criminal trial. In Raymond George Murray 1982 7A Crim R48 Sinclair DCJ refused to admit polygraph evidence tending to support the defense. The judge rejected the evidence because
- The veracity of the accused and the weight to be given to his evidence, and other witnesses called in the trial, was a matter for the jury.
- The polygraph "expert" sought to express an opinion as to ultimate facts in issue, which is peculiarly the province of the jury.
- The test purported to be expert evidence by the witness who was not qualified as an expert, he was merely an operator and assessor of a polygraph. The scientific premise upon which his assessment was based had not been proved in any Court in Australia.
- Devoid of any proved or accepted scientific basis, the evidence of the operator is hearsay which is inadmissible.
The Court cited, with approval, the Canadian case of Phillion v R 1978 1SCR 18.
Lie detector evidence is currently inadmissible in New South Wales courts under the Lie Detectors Act. Under the same act, it is also illegal to use lie detectors for the purpose of granting employment, insurance, financial accommodation, and several other purposes for which lie detectors may be used in other jurisdictions. 
Contrary to popular belief, a security clearance may not be revoked based solely on polygraph results. However, a person's access to sensitive information may be denied if the polygraph results are not favorable. In addition, persons being considered for a government position or job may be denied the employment, if the position specifically requires successful completion of a polygraph examination. It is difficult to precisely determine the effectiveness of polygraph results for the detection or deterrence of spying. It is inadmissible as evidence in most federal courts and military courts martial. The polygraph is more often used as a deterrent to espionage rather than detection. One exception to this was the case of Harold James Nicholson, a CIA employee later convicted of spying for Russia. In 1995, Nicholson had undergone his periodic five year reinvestigation where he showed a strong probability of deception on questions regarding relationships with a foreign intelligence unit. This polygraph test later launched an investigation which resulted in his eventual arrest and conviction. In most cases, however, polygraphs are more of a tool to "scare straight" those who would consider espionage. Jonathan Pollard was advised by his Israeli handlers that he was to resign his job from American intelligence if he was ever told he was subject to a polygraph test. Likewise, John Anthony Walker was advised by his handlers not to engage in espionage until he had been promoted to the highest position for which a polygraph test was not required, to refuse promotion to higher positions for which polygraph tests were required, and to retire when promotion was mandated.  As part of his plea bargain agreement for his case of espionage for the Soviet Union Robert Hanssen would be made to undergo a polygraph at any time as a means of damage assessment. In Hanssen's 25-year career with the FBI, not once was he made to undergo a polygraph.
Alternatively, the use of polygraph testing, where it causes desperation over dismissal for past dishonesty, may encourage spying. For example, Edward Lee Howard was dismissed from the CIA when, during a polygraph screening, he truthfully answered a series of questions admitting to minor crimes such as petty theft and drug abuse. In retaliation for his perceived unjust punishment for minor offenses, he later sold his knowledge of CIA operations to the Soviet Union. 
It is also worth noting that polygraph tests may not deter espionage. From 1945 to the present, at least six Americans have committed espionage while successfully passing polygraph tests. Notable cases of two men who created a false negative result with the polygraphs were Larry Wu-Tai Chin and Aldrich Ames. Ames was given two polygraph examinations while with the CIA, the first in 1986 and the second in 1991. The CIA reported that he passed both examinations after experiencing initial indications of deception.  According to a Senate investigation, an FBI review of the first examination concluded that the indications of deception were never resolved.  The Senate committee reported that the second examination, at a time when Ames was under suspicion, resulted in indications of deception and a retest a few days later with a different examiner. The second examiner concluded that there were no further indications of deception. In the CIA's analysis of the second exam, they were critical of their failure to convey to the second examiner the existing suspicions. Ana Belen Montes, a Cuban spy, passed a counterintelligence scope polygraph test administered by DIA in 1994.
Despite these errors, in August 2008, the US Defense Intelligence Agency announced that it would subject each of its 5,700 prospective and current employees to polygraph testing at least once annually.  This expansion of polygraph screening at DIA occurred while DIA polygraph managers ignored documented technical problems discovered in the Lafayette computerized polygraph system.  DIA uses computerized Lafayette polygraph systems for routine counterintelligence testing. The impact of the technical flaws within the Lafayette system on the analysis of recorded physiology and on the final polygraph test evaluation is currently unknown. 
In 2012, a McClatchy investigation found that the National Reconnaissance Office was possibly breaching ethical and legal boundaries by encouraging its polygraph examiners to extract personal and private information from DoD personnel during polygraph tests that purported to be limited to counterintelligence issues.  Allegations of abusive polygraph practices were brought forward by former NRO polygraph examiners. 
Most polygraph researchers have focused more the exam's predictive value on a subject’s guilt. However, there have been no empirical theories established to explain how a polygraph measures deception. Recent research indicates that Functional Magnetic Resonance Imaging (fMRI) may benefit in explaining the psychological correlations of polygraph exams. It could also explain which parts of the brain are active when subjects use artificial memories. Most brain activity occurs in both sides of the prefrontal cortex, which is linked to response inhibition. This indicates that deception may involve inhibition of truthful responses. Recalling artificial memories are known to activate the posterior cingulate cortex. However, fMRIs are limited by being expensive, immobile, and having inconsistent lying responses. Some researchers believe that reaction time (RT) based tests may replace polygraphs in concealed information detection. RT based tests differ from polygraphs in stimulus presentation duration, and can be conducted without physiological recording as subject response time is measured via computer. However, researchers have found limitations to these tests as subjects voluntarily control their reaction time, deception can still occur within the response deadline, and the test itself lacks physiological recording.
Earlier societies utilized elaborate methods of lie detection which mainly involved torture; for instance, the Middle Ages used boiling water to detect liars as it was believed honest men would withstand it better than liars. Early devices for lie detection include an 1895 invention of Cesare Lombroso used to measure changes in blood pressure for police cases, a 1904 device by Vittorio Benussi used to measure breathing, and an abandoned project by American William Moulton Marston which used blood pressure to examine German prisoners of war (POWs).  Marston’s machine indicated a strong positive between systolic blood pressure and lying.
Marston wrote a second paper on the concept in 1915, when finishing his undergraduate studies. He entered Harvard Law School and graduated in 1918, re-publishing his earlier work in 1917. Marston's main inspiration for the device was his wife, Elizabeth Holloway Marston. "According to Marston’s son, it was his mother Elizabeth, Marston’s wife, who suggested to him that 'When she got mad or excited, her blood pressure seemed to climb'" (Lamb, 2001). Although Elizabeth is not listed as Marston’s collaborator in his early work, Lamb, Matte (1996), and others refer directly and indirectly to Elizabeth’s work on her husband’s deception research. She also appears in a picture taken in his polygraph laboratory in the 1920s (reproduced in Marston, 1938)."  
Despite his predecessor's contributions, Marston styled himself the "father of the polygraph." (Today he is often equally or more noted as the creator of the comic book character Wonder Woman.) Marston remained the device's primary advocate, lobbying for its use in the courts. In 1938 he published a book, The Lie Detector Test, wherein he documented the theory and use of the device. In 1938 he appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.   
A device recording both blood pressure and breathing was invented in 1921 by John Augustus Larson of the University of California and first applied in law enforcement work by the Berkeley Police Department under its nationally renowned police chief August Vollmer.  Further work on this device was done by Leonarde Keeler.  As Larson's protege, Keeler updated the device by making it portable and added the galvanic skin response to it in 1939. His device was then purchased by the FBI, and served as the prototype of the modern polygraph. 
Several devices similar to Keeler's polygraph version included the Berkeley Psychograph, a blood pressure-pulse-respiration recorder developed by C. D. Lee in 1936 and the Darrow Behavior Research Photopolygraph, which was developed and intended solely for behavior research experiments.  
A device which recorded muscular activity accompanying changes in blood pressure was developed in 1945 by John E. Reid, who claimed that greater accuracy could be obtained by making these recordings simultaneously with standard blood pressure-pulse-respiration recordings. 
Society and culture
Lie detection has a long history in mythology and fairy tales; the polygraph has allowed modern fiction to use a device more easily seen as scientific and plausible. Notable instances of polygraph usage include uses in crime and espionage themed television shows and some daytime television talk shows, cartoons and films. The most notable polygraph TV show is Lie Detector, which first aired in the 1950s created and hosted by Ralph Andrews. In the 1960s Andrews produced a series of specials hosted by Melvin Belli. In the 1970s the show was hosted by Jack Anderson. In 1998 TV producer Mark Phillips with his Mark Phillips Philms & Telephision put Lie Detector back on the air on the FOX Network—on that program Ed Gelb with host Marcia Clark questioned Mark Fuhrman about the allegation that he "planted the bloody glove". Later Phillips produced Lie Detector as a series for PAX/ION—some of the guests included Paula Jones, Reverend Paul Crouch accuser Lonny Ford, Ben Rowling, Jeff Gannon and Swift Boat Vet, Steve Garner.
FOX has taken this one step further with their game show The Moment of Truth, which pits people's honesty against their own sense of modesty, propriety and other values. Contestants are given a polygraph test administered by a polygraph expert in a pre-screening session during which they answer over 50 questions. Later, they must sit in front of a studio audience that including their friends and family for the televised portion of the show. They need only answer 21 answers truthfully "as determined by the polygraph" to win $500,000. The questions get more personal or revealing as they advance. Most polygraph experts caution that the techniques used on Moment of Truth do not conform to accepted methods of polygraphy.
In one MacGyver episode 'Slow Death', MacGyver assists the Indian tribesmen by improvising a polygraph to weed out the crooked doctor. This is made possible by using an analog sphygmomanometer to monitor blood pressure change, and an electronic alarm clock to detect sweat. To test its reliability, MacGyver asked a passenger on the train a few "placebo" questions. The culprit was only discovered when he was trying to hide his crime, thus his sweat triggered the alarm clock and blood pressure climbed up.
In the movie Harsh Times the protagonist, played by actor Christian Bale, is caught trying to "beat" a polygraph test during a pre-employment screening for a federal law enforcement job. He stores a tack in the toe of his shoe and uses the pain sensation to mask his true apprehension of certain questions. The polygrapher is immediately suspicious and threatens to terminate the test.
In the movie Ocean's 13, one of the characters beats a polygraph test by stepping on a tack when answering truthfully, which supposedly raises the polygraph's readings for the truthful answers so they equal the deceptive ones.
In the television series Profit, there is a memorable sequence at the end of episode "Healing" where the eponymous character, Jim Profit, manages to fool a polygraph. He does that by putting a nail through the sole of his shoe and pushing it inside of his heel while answering every question in order to even out the readings. This scene is very graphic, especially for its time, 1996. During a voice-over, Profit explains the theory behind the polygraph and the flaws he intends to exploit in it.
In the 20th episode of The Americans, " Arpanet ", Nina, a KGB double agent, misleads her FBI handler after receiving coaching on how to beat the polygraph from Oleg, her Soviet superior. Oleg describes the machine as being similar to a camera in that it doesn't know if the subject's smiles convey genuine happiness. He also uses the asp killing Cleopatra as a metaphor, stating it only killed her when she moved. One technique suggested to Nina is visualizing her KGB superior in the room, as well as clenching her anus. She appears to utilize and benefit from these techniques as she passes the test.
In episode 93 of the US popular science show MythBusters, they attempted to fool the polygraph by using pain to try to increase the readings when answering truthfully (so the machine will supposedly interpret the truthful and non-truthful answers as the same.) They also attempted to fool the polygraph by thinking happy thoughts when lying and thinking stressful thoughts when telling the truth to try to confuse the machine. However, neither technique was successful for a number of reasons. Michael Martin correctly identified each guilty and innocent subject. The show also noted the opinion that, when done properly, polygraphs are correct 80–99% of the time. 
Hand-held lie detector for US military
A hand-held lie detector is being deployed by the US Department of Defense according to a report in 2008 by investigative reporter Bill Dedman of MSNBC. The Preliminary Credibility Assessment Screening System, or PCASS, captures less physiological information than a polygraph, and uses an algorithm, not the judgment of a polygraph examiner, to render a decision whether it believes the person is being deceptive or not. The device will be used first in Afghanistan by US Army troops. The Department of Defense ordered its use be limited to non-US persons, in overseas locations only. 
Polygraphy has been faulted for failing to trap known spies such as double-agent Aldrich Ames, who passed two polygraph tests while spying for the Soviet Union.   However Ames did fail several tests while at the CIA that were never acted on.  Other spies who passed the polygraph include Karl Koecher, Ana Belen Montes,  and Leandro Aragoncillo.  However, CIA spy Harold James Nicholson failed his polygraph examinations, which aroused suspicions that led to his eventual arrest.  Polygraph examination and background checks failed to detect Nada Nadim Prouty, who was not a spy but was convicted for improperly obtaining US citizenship and using it to obtain a restricted position at the FBI. 
The polygraph also failed to catch Gary Ridgway, the "Green River Killer". Another suspect allegedly failed a given lie detector test, whereas Ridgway passed. Ridgway passed a polygraph in 1984; he confessed almost 20 years later when confronted with DNA evidence.  In the interim he had killed seven additional women.
Conversely, innocent people have been known to fail polygraph tests. In Wichita, Kansas in 1986, because he failed two polygraph tests (one police administered, the other given by an expert that he had hired), Bill Wegerle had to live under a cloud of suspicion of murdering his wife Vicki Wegerle, although he was neither arrested nor convicted of her death. In March 2004, evidence surfaced connecting her death to the serial killer known as BTK, and in 2005 DNA evidence from the Wegerle murder confirmed that the BTK Killer was Dennis Rader  and established Bill Wegerle's innocence.
Prolonged polygraph examinations are sometimes used as a tool by which confessions are extracted from a defendant, as in the case of Richard Miller, who was persuaded to confess largely by polygraph results combined with appeals from a religious leader.
In the high-profile disappearance of 7-year-old Danielle van Dam of San Diego in 2002, police suspected neighbor David Westerfield; he became the prime suspect when he allegedly failed a polygraph test. He was ultimately tried and convicted of kidnapping and first degree murder.
- Bogus pipeline
- Cleve Backster
- Ecological fallacy
- Ronald Pelton
- Silent Talker Lie Detector
- Voice stress analysis
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