A scene from “Arrested Development” (2004).
A scene from “Arrested Development” (2004). Despite their flaws, lie detectors have seeped into popular culture

You’ll be familiar with the scene. A hard-nosed cop, a nervous suspect, the slow scratching of needles. In the hundred years since it was invented, the polygraph machine – or lie detector – has oozed into every crevice of America’s justice system and popular culture, appearing in true crime documentaries, blockbuster movies and daytime TV shows, as well as interrogation rooms.

What you might not know, however, is that lie detectors are increasingly being used in the UK too. A lack of transparency from police forces means it’s difficult to know exactly how the polygraph is being used, and to what extent. What’s certain is that convicted terrorists and sex offenders are now being tested on the polygraph after parole to make sure they’re complying with the terms of their probation. In October 2023, a Ministry of Justice report revealed that a total of 88 lie detector tests had been carried out on 39 people since June 2021, leading to four paroled terrorism offenders being sent back to prison – one for failing to comply with the polygraph test, three for revealing “risk-related information” during one of their tests.

Good news, on the surface. The system works! But there’s a problem. Ever since it was invented, the polygraph test has been repeatedly debunked. It’s inaccurate, unscientific and biased. Results vary wildly depending on who’s conducting the test, and who’s taking it. It has a tendency to produce false positives or coerce innocent people into admitting things they didn’t do. It has helped put criminals behind bars, but it’s also been used to perpetrate gross miscarriages of justice.

“The scientific validity of the polygraph test is highly questionable,” Marion Oswald and Kyriakos Kotsoglou, who research the use of lie detectors in the English penal system at the University of Northumbria’s law school, tell me. “Even the UK Government focuses on the utility of the polygraph (the increased number of confessions), not on its validity.” It puts pressure on people to tell you things, but it can’t tell you whether those things are actually true.

As far back as 1965, a US committee on government operations concluded that “people have been deceived by a myth that a metal box in the hands of an investigator can detect truth or falsehood”. The UK government claims it’s 80 to 90 per cent accurate, but rigorous scientific research puts that figure as low as 65 per cent.

So why are governments and police forces in the UK increasing their use of the lie detector?

A more human method of solving crime?

To answer that question, we have to go back to the 1920s and to John Larson, a rookie police officer in Berkeley, California. Larson was by all accounts a terrible cop. He missed burglaries while getting milkshakes, got into fistfights with his colleagues and managed to crash two patrol cars in one day while learning to drive. He wanted to be a criminologist and saw his time in the police as a way to get hands-on knowledge of crime before moving into academia. And he happened to land at one of the most forward-thinking police forces in the country.

The Berkeley Police Department was run by August Vollmer, now considered the “father of modern policing”. He was one of the first police chiefs in America to give his officers radios and vehicles to cover more ground, and he pioneered the use of crime scene photography and finger-printing. In an attempt to make policing more efficient and humane, he hired college graduates like Larson instead of the more thuggish types who populated forces at the turn of the century.

In the spring of 1921, Vollmer was flicking through a criminology journal looking for a paper he’d submitted when he chanced on an article by William Moulton Marston, a Harvard psychologist who’d noticed that people’s blood pressure seemed to rise when they told untrue stories. (Marston would go on to create the comic book character Wonder Woman and her “lasso of truth” which compelled all who touched it to honesty.)

Vollmer wondered, as he often did, whether this insight could be used to solve crimes, and he summoned John Larson into his office. Together, they came up with a plan to systematise Marston’s insight about lying and blood pressure, and turn it from a subjective observation into an objective measurement that could be used in criminal investigations.

Larson went away and a few weeks later came back with an ugly-looking device that combined a blood pressure cuff with rubber tubes that wrap around a subject’s chest to measure breathing, two moving styluses and a rolling drum of charcoal-blacked paper. The first lie detector machine.

Here’s how it’s meant to work. A polygraph exam begins with a series of “yes or no” control questions with known answers: is your name John? Are you sitting in a chair? These are to set a baseline for how a person’s body will react when they’re speaking the truth. That’s followed by target questions: did you steal the car? Did you kill him? By comparing the record of a person’s pulse and blood pressure between the baseline questions and the target questions, a skilled polygraph examiner is meant to be able to tell when they’re lying.

It relies on liars being nervous. But that’s a dangerous fallacy. Honest people can be nervous about being wrongly accused, which is one of the reasons the polygraph has coerced hundreds of innocent people into confessing to crimes they didn’t commit, as logged by the attorney-led NGO the Innocence Project. Some people can control their emotions well enough to beat a polygraph test. Others simply don’t feel those emotions in the first place. With a bit of training, anyone can learn to beat a polygraph test, for instance by exaggerating their responses to the baseline questions so their lies don’t stand out. There’s no tell-tale sign of lying that’s true of everyone all the time – no
Pinocchio’s nose.

John Larson figured all that out pretty quickly as he began to use the polygraph on real-world crimes, starting with petty thefts in the women’s dorms at the University of Berkeley. Already, the problematic dynamics that the machine introduced were becoming apparent – the first real-world polygraph test Larson ever conducted was on Margaret Taylor, a college student 10 years his junior who’d had some jewellery stolen from her room. A year later, Larson married her.

He had begun the experiment with noble intentions. Larson wanted his lie detector to create a more humane method of solving crimes – to replace the cruel beatings and the third-degree interrogations that his police peers would dole out. But in that first year, as word of the polygraph spread and it began to be used in murder investigations and tabloid scandals, it grew too fast for him to control. He started to have doubts about the machine, particularly when Henry Wilkens – a San Francisco mechanic accused of plotting his wife’s death – passed a polygraph test despite clear evidence that he was involved. But by then it was too late. The device became, in Larson’s view, “a Frankenstein’s monster”. And in his mind, it was pretty clear who was to blame for that.

He’d first crossed paths with Leonarde Keeler when the latter was a sickly but precocious high school student – a family friend of Larson’s boss, Vollmer. The young Keeler was an amateur magician adept at sleight of hand. But from the moment Vollmer invited him to watch Larson interrogating a suspect in the basement of Berkeley’s City Hall, Keeler was hooked on the lie detector. It became his new obsession, and as Larson tried to firm up the science of the machine, Keeler began streamlining the machinery, with a view to making something he could sell.

It drove a wedge between the two men. Keeler was soon running his own investigations, despite a lack of scientific or police training, and making headlines with sensationalist claims. He commercialised the machine, selling units to police forces and businesses all over America. He was probably responsible for the first uses of the lie detector in the UK, too. Although the machine never really caught on in the same way here, we know that Keeler sold one device to the department store Selfridges.

A potent and popular weapon

The polygraph has never been admissible in federal court in the US, but thanks to Keeler it infiltrated (Larson would say infected) every other part of American society. Police forces loved it because it was a way of extracting a confession from a suspect, rather than having to go to the expense of collecting evidence and preparing for a trial. You couldn’t force someone to take a polygraph test, but refusing would look very incriminating.

Employers loved it because they could use it to strike fear into the hearts of any employees considering sneaking money from the till. Until the practice was banned in the 1980s, large companies in the US ran regular screening tests on employees at all levels. At one point, McDonald’s was running lie detector tests on its cashiers.

Governments learned to love it, too. During the “red scare” of the 1950s, when US Senator Joseph McCarthy whipped America into a frenzied anti-communist witch hunt, the polygraph became a potent tool: you could use it to collect compromising material on government employees to keep them loyal, or as a potent weapon against your political enemies. And if you’re looking for the reason why their use is growing in the UK, that may be part of the answer.

Leonarde Keeler was the first enterprising soul to see the commercial potential of the lie detector, but he was far from the last. The last hundred years have seen waves of investment and research into different types of deception detection: polygraphs in the 1920s, infrared lasers to measure body temperature in the 1970s, voice stress analysis in the 1990s, micro-expressions and brain scans in the 2000s and pupil dilation in the 2010s, along with the use of artificial intelligence to combine data from multiple sources in order to produce “honesty scores”.

But no matter what their creators claim, these technologies all suffer from the same fatal flaw as the polygraph. There is no such thing as a reliable lie detector. They are often just an elaborate piece of theatre – a sleight of hand like the ones Keeler used to perform to impress his classmates. A confidence trick. Sometimes, the mere mention of a lie detector can be enough to cause someone to confess: in the 1980s, police officers in Detroit managed to get a suspect to confess using a photocopier. They put his hand on it, and then got it to print out sheets of paper with “He’s Lying” written on them.

I spent two years researching the past, present and future of deception detection for my book Tremors in the Blood, and I quickly noticed a pattern. Investment in lie detectors rises at times of political and social tension: the biggest spike in interest came in the years after 9/11. There were also surges in the early 1980s and the mid-1990s, correlating with Republican governments and foreign military campaigns.

They also tend to be targeted at the most vulnerable in society, or convenient scapegoats. In Larson and Keeler’s time that was largely young women and the mentally ill, in the 1950s it was suspected communists and homosexuals, and in the 2000s it was suspected terrorists. Today, it’s asylum seekers and migrants. The latest lie detector technologies are being designed for use at borders in Europe and the US.

Infiltrating the UK

Governments like to use lie detectors as a propaganda tool, to show they’re being tough on whatever group is the scapegoat of the moment. Between 2007 and 2010, for instance, a pilot scheme saw UK councils using voice stress analysis to try and identify benefits cheats over the phone. After 9/11, the US government invested millions in training border guards in how to read “microexpressions” – almost imperceptible facial movements that, according to researcher Paul Ekman, could be used to tell when someone was lying. In the six years after the scheme was launched in 2006, it stopped approximately 30,000 people a year, none of whom were terrorists. Meanwhile, at least 16 terrorists managed to enter the country undetected.

Right now, the UK has a government that wants to show it’s being tough on crime. It wants positive tabloid headlines about how it’s clamping down on terrorists and sex offenders. The headline-grabbing nature of the lie detector – our fascination with it – makes it an easy way of getting that coverage. The problems come when institutions like government and the police start to believe their own lies.

We don’t really know how the polygraph is being used in the UK today. In 2020, Northumbria law researchers Oswald and Kotsoglou sent Freedom of Information requests to every UK police force to try and find out. There was a worrying lack of transparency: 37 out of 46 would neither confirm nor deny if they were using the machine.

Perhaps because the polygraph hasn’t caught on here until recently, there’s not really a legal framework for how, when and if it should be used. The National Police Chiefs Council strongly discourages its use, but there’s currently nothing to stop police forces from trying it during interrogations as their US colleagues do. And because the lie detector has been positioned as protecting the British public from sex offenders and terrorists, it’s hard for politicians to urge caution or restraint. When the Scottish National Party blocked the use of polygraphs on terror suspects in Scotland because of concerns about their merits, the party was attacked by the Sun and by Conservative MPs: “weak on terrorism, weak on security”.

The problem isn’t the use of polygraphs per se. “Polygraph testing is an interrogation tool, not a lie detector, as demonstrated by the emphasis on disclosures made during the interview process,” Oswald and Kotsoglou explain. “Questions remain about whether those disclosures would have been made in any event through normal offender management processes, and whether the process relies on convincing offenders that the machine can detect lying.” Defenders of the use of lie detector screening tests will tell you they’re just part of a suite of different tools used to assess whether someone is suitable for parole.

But Kotsoglou calls it “zombie forensics”. Like the security theatre that pervaded airports after 9/11, it risks giving investigators a false sense of security – that if the machine says someone’s telling the truth, then they must be. “We are already on the slippery slope with regards to the polygraph,” Kotsoglou told me in 2020. “This becomes a threat in terrorism. A false sense of security could have literally fatal consequences.” The same could be said of sex offences.

When you bring flawed technology into a previously human process, there’s a natural instinct to give it more weight than it deserves, or to use it as psychological prop or a propaganda weapon. That’s the painful lesson John Larson and Leonarde Keeler learned after they unleashed the polygraph on the world. We’d do well to learn it too.

This article is from New Humanist's spring 2024 issue. Subscribe now.