# Why is lie detector technology not considered viable in a USA court of law? **URL:** \ **Category:** Factual Questions\ **Created:** [July 29, 2022, 8:11am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764 "2022-07-29T08:11:34Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [July 29, 2022, 1:05pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/21 "2022-07-29T13:05:22Z")
On this last point, I read in a cop’s memoir (don’t remember which) that they used to get good results by having the suspect sit next to the office copy machine with a metal pasta strainer on his head. They’d have a sheet of paper on the glass with the lid closed, and every time they thought the suspect was jerking them around, they pressed the copy button and a fresh sheet would come out with the big word LIE on it. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [July 29, 2022, 1:06pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/22 "2022-07-29T13:06:46Z")
> [@Saint\_Cad](#): > > I was going to say, if we don’t allow lie detectors then why do we still allow drug-dog indications as legal justifications for searches? Because a search is not a conviction and other legal justifications for searches aren’t subject to “proven beyond reasonable doubt”-standards either. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [July 29, 2022, 1:08pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/23 "2022-07-29T13:08:10Z")
> [@Cervaise](#): > > I read in a cop’s memoir (don’t remember which) that they used to get good results by having the suspect sit next to the office copy machine with a metal pasta strainer on his head… This is a widely retold urban legend. I don’t think it has ever been reliably traced back to any real event. > **[Colander Lie Detector](https://www.snopes.com/fact-check/next-case-on-the-court-colander/)** > > Did the police fool a criminal into giving a confession through a ruse involving a photocopier and a colander? ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [July 29, 2022, 1:09pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/24 "2022-07-29T13:09:45Z")
> [@Cervaise](#): > > On this last point, I read in a cop’s memoir (don’t remember which) that they used to get good results by having the suspect sit next to the office copy machine with a metal pasta strainer on his head. They’d have a sheet of paper on the glass with the lid closed, and every time they thought the suspect was jerking them around, they pressed the copy button and a fresh sheet would come out with the big word LIE on it. Yes, a lot of cops have told this story. It’s an urban legend. I don’t believe it happened. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [July 29, 2022, 1:14pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/25 "2022-07-29T13:14:48Z")
> [@naita](#): > > Because a search is not a conviction and other legal justifications for searches aren’t subject to “proven beyond reasonable doubt”-standards either. So basically it is allowed to give cops their justification for fishing expeditions and bypass the 4th Amendment. Similar to sniff sniff “I smell alcohol.” ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [July 29, 2022, 1:17pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/26 "2022-07-29T13:17:51Z")
> [@SmartBulbInc](#): > > Here we have this awesome technology that is able to literally tell whether a defendant is lying or not. This is false. How did you get this impression? We have technology that can read certain biological processes, like heart rate, blood pressure, respiration, and skin conductivity. Everything else is voodoo and is subjective based on how the examiner conducts the test and interprets the results. The science of reading the biological processes is completely sound; doctors do it every day. But trying to interpret them to indicate that someone is lying is not. It’s no better than, “He wouldn’t look me in the eye so he must be lying.” **[The Truth About Lie Detectors (aka Polygraph Tests)](https://www.apa.org/topics/cognitive-neuroscience/polygraph#:~:text=The%20instrument%20typically%20used%20to,today%20use%20computerized%20recording%20systems.)** ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [July 29, 2022, 1:18pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/27 "2022-07-29T13:18:17Z")
Re the UL: okay, fair enough. The memoir claimed it as fact, but cops do like their yarns. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [July 29, 2022, 1:18pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/28 "2022-07-29T13:18:43Z")
> [@Saint\_Cad](#): > > So basically it is allowed to give cops their justification for fishing expeditions and bypass the 4th Amendment. Similar to sniff sniff “I smell alcohol.” I’d ask what your standard for “reasonable” would be to balance effective policing and privacy, but it seems a bit off topic and I agree with you that police often abuse the available standards. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [July 29, 2022, 1:26pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/29 "2022-07-29T13:26:05Z")
> [@Peter\_Morris](#): > > > [@Cervaise](#): > > > > On this last point, I read in a cop’s memoir (don’t remember which) that they used to get good results by having the suspect sit next to the office copy machine with a metal pasta strainer on his head. They’d have a sheet of paper on the glass with the lid closed, and every time they thought the suspect was jerking them around, they pressed the copy button and a fresh sheet would come out with the big word LIE on it. > > Yes, a lot of cops have told this story. It’s an urban legend. I don’t believe it happened. - I wonder if it actually happened once as a “I had a suspect so dumb…” story and it took on a life of it’s own. Look at the insane stories scammers come up with and people fall for 'em. Why not a rigged copier? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 29, 2022, 1:54pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/30 "2022-07-29T13:54:19Z")
> [@Mean\_Mr.Mustard](#): > > The real question is why polygraphs are being used at all. According to Wikipedia, > > _US law enforcement] and federal government agencies such as the FBI, NSA, CIA, and many police departments such use polygraph examinations to interrogate suspects and screen new employees._ > > mmm We Computer Science folk call this “security theater”. Pretending you’re doing something to increase security without the bother of actually doing things right. Institutional inertia and just plain stupidity are powerful forces. Remember, Israeli spy [Jonathan Pollard](https://en.wikipedia.org/wiki/Jonathan_Pollard) lied all over the place. A decent vetting process would have found him out before he was hired. The CIA’s tests found he was lying so they kicked him out. So he went to Naval Intelligence and managed to pass (more or less) polygraphs after that. Of course the CIA didn’t tell the Navy about what they found. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [July 29, 2022, 2:09pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/31 "2022-07-29T14:09:06Z")
> [@ftg](#): > > Remember, Israeli spy [Jonathan Pollard](https://en.wikipedia.org/wiki/Jonathan_Pollard) lied all over the place. A decent vetting process would have found him out before he was hired. The CIA’s tests found he was lying so they kicked him out. So he went to Naval Intelligence and managed to pass (more or less) polygraphs after that. Of course the CIA didn’t tell the Navy about what they found. But again, I’m quite certain the CIA know that polygraph tests are unreliable, and the polygraph may have been used appropriately and exactly as intended here simply to put pressure on a subject to reveal something or to indicate that he _may_ be hiding something and cannot be trusted. What happened subsequently at the navy may not necessarily be that they used the polygraph to positively _clear_ him, just that he had got wise to not letting the polygraph disconcert him, and it did not _expose_ him. No doubt they also used other interrogation techniques to put pressure on him - the fact that none of those worked either to expose him on this occasion does not invalidate all of these techniques. I’m not ruling out the fact that the navy may have been using polygraphs inappropriately as a _positive_ vetting tool, rather than just one of a range of techniques to put pressure on a subject; but I don’t necessarily see any evidence of that from this outcome. ---
**Author:** ![Retzbu\_Tox](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/retzbu_tox/32/11829_2.png) [@Retzbu\_Tox](https://boards.straightdope.com/u/Retzbu_Tox)\ **Post date:** [July 29, 2022, 3:31pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/32 "2022-07-29T15:31:27Z")
Assuming there have been enough serious answers, so I can now make a non-serious comment… I wanna start a religion where we use lie detectors during confession. Wait… what’s that? You say it’s been done already? Phooey. ---
**Author:** ![tofor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tofor/32/13727_2.png) [@tofor](https://boards.straightdope.com/u/tofor)\ **Post date:** [July 29, 2022, 3:57pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/33 "2022-07-29T15:57:39Z")
> [@smithsb](#): > > I could see working a polygraph into a TV game show. Hook it to the contestant or to the Host when he/she says, “Door number one, door number two, or door number three?” [the Monty Hall dilemma]. > > A court of law, nope nope nope. A polygraph was the basis for a really terrible TV show. I remember seeing this when it was on, and just cringing the whole time. It was awful. > **[The Moment of Truth (American game show)](https://en.wikipedia.org/wiki/The_Moment_of_Truth_(American_game_show))** > > The Moment of Truth is an American game show based on the Colombian Nada más que la verdad format ("Nothing but the Truth"). Contestants answer a series of 21 increasingly personal and embarrassing questions to receive cash prizes. The show was hosted by Mark L. Walberg and ran on the Fox network from January 23, to August 28, 2008. > On February 1, 2008, Fox ordered an additional 13 episodes of the show, bringing its episode order to 23. It was supposed to be on Fox's fall lineup, but was pushed... ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [July 29, 2022, 4:19pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/34 "2022-07-29T16:19:36Z")
> [@Peter\_Morris](#): > > How was the accuracy determined? Their accuracy would rate a big 0. It doesn’t matter what anybody claims about these devices, they don’t detect lies. They don’t have any devices that detect a lie because there is no way to do that. Whether it’s the traditional polygraph or some other device analyzing voice patterns or your eyes, none of them have a lie sensor, not one. If it really does concern you that a box of junk might be somehow detecting lies, please note that these devices don’t come with red “lie” and green “truth” LEDs, their results have to be interpreted by polygraph operators, and not one of them will tell you how they actually do those interpretations, because they are just guessing. The same output from lie detector tests will be interpreted as truthful or dishonest by the operators, who themselves are easily manipulated to give the result that desired by whoever is paying them. There is no more science or accuracy to these things than a child’s origami fortuneteller. ---
**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\ **Post date:** [July 29, 2022, 4:26pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/35 "2022-07-29T16:26:45Z")
Taking a beta blocker before a polygraph pretty much insures you’ll pass. Giving credence to a device that can be defeated by a dose of high blood pressure medicine seems…unwise. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [July 29, 2022, 4:40pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/36 "2022-07-29T16:40:57Z")
> [@SmartBulbInc](#): > > This one is a little more understandable. However, there is one problem with this argument: The same can be said about the entire prosecution process. If refusing to speak under oath isn’t a crime for the goverment, why is being forced to use a lie detect one? I don’t understand this comment. An accused persopn in the US has the absolute right to refuse to speak to police, and cannot be compelled to testify. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [July 29, 2022, 7:38pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/37 "2022-07-29T19:38:08Z")
> [@Czarcasm](#): > > From here: [Do Lie Detector Tests Really Work? | Psychology Today](https://www.psychologytoday.com/us/blog/the-nature-deception/202001/do-lie-detector-tests-really-work) > we learn that " The American Polygraph Association is the world’s leading association dedicated to the use of evidence-based scientific methods for credibility assessment. It is an organization whose members are largely polygraph examiners. They estimate the accuracy of the polygraph to be 87%. That is, in 87 out of 100 cases, the polygraph can accurately determine if someone is lying or telling the truth. Oddly enough, this is, it seems, an association of people who make a living off polygraphs, so probably want people to believe they work - and that’s their honest assessment. > [@Saint\_Cad](#): > > > [@naita](#): > > > > Because a search is not a conviction and other legal justifications for searches aren’t subject to “proven beyond reasonable doubt”-standards either. > > So basically it is allowed to give cops their justification for fishing expeditions and bypass the 4th Amendment. Similar to sniff sniff “I smell alcohol.” This exactly. I’m surprised nobody has mentioned the basic, fatal flaw. A polygraph indicates your responses, as we see on assorted TV shows, on a graph. Then an expert analyzes this graph and says what _they think_ the graph says. Contrary to popular TV shows, it’s not a flat line that goes crazy when you lie. The readings can be all over the place. As others pointed out, assorted other stressors can affect those readings. Some guy who is paid by the government, usually the prosecution, decides whether he thinks you are telling the truth. (At least the copy machine gave a yes-or-no answer). Then there’s observer bias. How much does the tester know? What have the police told them? Will they keep their job if they give too many “not guilty” verdicts? Will they get on the stand and admit it’s just a personal guess or assert it’s 100% accurate to naïve jurors - even though it is not? For someone like the FBI or CIA, who cares? So you reject 1/4 of honest candidates. Or, you weed out 3/4 of potential security risks. That’s better than nothing. It’s not the same as whether someone spends 10 years in jail or goes free. (One story I heard was to put something in your shoe to cause a bit of pain. Then hurt yourself when you answer truthful test questions, so the baseline is off enough to hide any possible lies.) ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [July 29, 2022, 7:45pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/38 "2022-07-29T19:45:59Z")
And don’t forget if you’re innocent you’re still guilty. You can be said to be cleared of the accused crime but still “concealing something”. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 29, 2022, 7:59pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/39 "2022-07-29T19:59:13Z")
> [@md-2000](#): > > For someone like the FBI or CIA, who cares? So you reject 1/4 of honest candidates. Or, you weed out 3/4 of potential security risks. That’s better than nothing. Is it better than nothing? Let’s say that instead of an orgasm test, those organizations instead use a coin test: For every candidate, they flip two coins, and if they both come up tails, the candidate is rejected. This would stop some nonzero number of spies, and only reject a quarter of honest applicants. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [July 29, 2022, 8:08pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/40 "2022-07-29T20:08:18Z")
Fun fact. The polygraph was invented by William Moulton Marston. William Moulton Marston is best known as the creator of Wonder Woman. Wonder Woman has a lasso of truth, which makes it impossible for people to tell a lie. [Previous page](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764.md?page=1) [Next page](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764.md?page=3)