# 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:** 15\ **Page:** 7
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [August 3, 2022, 7:57pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/121 "2022-08-03T19:57:15Z")
> **[Vintage 1970 Science Fair Lie Detector Kit By Radio Shack | #1869919936](https://www.worthpoint.com/worthopedia/vintage-1970-science-fair-lie-1869919936)** > > This is a vintage 1970 Science Fair Lie Detector Kit made by Radio Shack. It comes in the original box, has the lie detector box, the wires, instructions and other information sheets. It was tested an ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [August 3, 2022, 7:58pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/122 "2022-08-03T19:58:41Z")
> [@WhyKickAMooCow](#): > > So the strength of the device is the mystique and suggestibility that it works, the fact that it can not actually detect lies does not even come into it. One comment on the video puts it best: “The polygraph is useless as evidence, but is ultimately an incredible interrogation tool. She made great use of her time, and wreaked havoc on his psyche.” It is also useful in conning innocent people into believing that what they think is the real story _isn’t_, or that the court will believe this “evidence” over their own testimony so the best thing to do would be to take any deal the police give them and sign a fake confession. ---
**Author:** ![Esprise\_Me](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/esprise_me/32/2947_2.png) [@Esprise\_Me](https://boards.straightdope.com/u/Esprise_Me)\ **Post date:** [August 3, 2022, 8:10pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/123 "2022-08-03T20:10:48Z")
Yeah, given how much we know about how easy it is to coerce a false confession, I wouldn’t put too much stock in a confession obtained from someone who’d been told they failed the lie detector test. Unless in their confession they revealed things they couldn’t have known otherwise. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 3, 2022, 8:25pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/124 "2022-08-03T20:25:28Z")
Nothing is accurate enough for a Criminal Court, but some things are good enough to support a further investigation. “Hmm, he showed many of the signs of lying, maybe we should dig deeper, see what we can find” is one thing but “he furrowed his brow (etc, etc, etc) and thus he must be guilty!” is just wrong. ---
**Author:** ![The\_Other\_Waldo\_Pepper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_other_waldo_pepper/32/12370_2.png) [@The\_Other\_Waldo\_Pepper](https://boards.straightdope.com/u/The_Other_Waldo_Pepper)\ **Post date:** [August 4, 2022, 2:00am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/125 "2022-08-04T02:00:58Z")
> [@Saint\_Cad](#): > > I saw one claim that furrowing of the forehead = lie is the most accurate lie detector and that the Secret Service uses that fact in their investigations. Hell of a thing, Botox… ---
**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:** [August 4, 2022, 4:39am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/126 "2022-08-04T04:39:43Z")
> [@Dr\_Paprika](#): > > Go down the highway, three clicks past the coffee shop. Turn right at the big tree. …three clicks past the _Tim Horton’s_ Fixed it for you. > [@Esprise\_Me](#): > > Yeah, given how much we know about how easy it is to coerce a false confession, I wouldn’t put too much stock in a confession obtained from someone who’d been told they failed the lie detector test. Unless in their confession they revealed things they couldn’t have known otherwise. But presumably the jury would never hear the fact the defendant had taken a lie detector test, let alone failed it? ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [August 4, 2022, 4:48am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/127 "2022-08-04T04:48:21Z")
> [@md-2000](#): > > But presumably the jury would never hear the fact the defendant had taken a lie detector test, let alone failed it? If the prosecution builds their case around a confession in which the defendant was told that they had failed a test, then that fact _should_ come to the attention of the defense – either by the defendant telling their attorney about it, and/or during pre-trial discovery – and I’d expect the defense attorney to pursue getting the confession thrown as evidence. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 4, 2022, 4:54am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/128 "2022-08-04T04:54:20Z")
It is perfectly legal to lie to a perp to get him to confess. Sadly. ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [August 4, 2022, 4:55am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/129 "2022-08-04T04:55:46Z")
> [@DrDeth](#): > > It is perfectly legal to lie to a perp to get him to confess. But (and IANAL, so I’m genuinely asking), is it legal for law enforcement or the prosecution to withhold the details of the interrogation from the defense (and, by extension, from the court)? ---
**Author:** ![crowmanyclouds](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crowmanyclouds/32/19884_2.png) [@crowmanyclouds](https://boards.straightdope.com/u/crowmanyclouds)\ **Post date:** [August 4, 2022, 5:46am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/130 "2022-08-04T05:46:22Z")
I remember those! It had that cool packaging so when you flipped the box over it was also an E-Meter! 'Cause when you get down to it Polygraphy machines and E-Meters are both equally effective at detecting what they detect . . . which is what ever the operator needs it to detect. ---
**Author:** ![Esprise\_Me](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/esprise_me/32/2947_2.png) [@Esprise\_Me](https://boards.straightdope.com/u/Esprise_Me)\ **Post date:** [August 4, 2022, 6:41am UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/131 "2022-08-04T06:41:09Z")
It depends. I believe in some states, you can’t introduce the results of a polygraph at all. But in most states, including mine, you can introduce the results of a polygraph if both sides agree to it. Occasionally, under certain special circumstances, certain polygraph results may be admissible over one party’s objection. As a defense attorney, if you believe your client was tricked/badgered/coerced into falsely confessing by a police officer who told him he failed the lie detector test, you have two separate issues to consider: 1. CAN you get into evidence what the cop said about failing the lie detector test, and if so, 2. SHOULD you? If the jury is made up of people who are as skeptical of polygraphs as I am, the answer to #2 is yes. I would give less weight to a confession that was made by someone who had just been told he failed the polygraph than a confession given freely, and I wouldn’t find the actual results of the polygraph very persuasive either way. So if you couldn’t get the judge to suppress the confession entirely (and you probably couldn’t, unless we add some more facts to this scenario), you’re probably better off getting the whole story before the jury of Esprise Me clones. But most jurors won’t think like me. At least some jurors will think the polygraph has some value, so you’d be rolling the dice by letting any mention of the polygraph come into evidence. So you have to make a judgment call, assuming the law leaves open the possibility in the first place. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 4, 2022, 5:49pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/132 "2022-08-04T17:49:40Z")
The entire interrogation is available to the defense. I leave it up to one of our lawyers to say if using a polygraph like that could be successfully used by the Defense. ---
**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:** [August 4, 2022, 6:44pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/133 "2022-08-04T18:44:27Z")
To my mind, the trick would be - _why_ did the perp fail (or allegedly fail) the polygraph test. If it’s the scenario where the officer glances at the polygraph and says “you’re lying”, or worse yet, does not even study the result, then presumably it would be safe to argue it was coercion. Even more so if they followed it up with - “with this as evidence, you’re going to get convicted and it will go hard on you if you don’t confess” the usual interrogatory bullsh… Then maybe the argument about being coerced into a confession will fly with the jury. Otherwise, i suppose it’s up to the judge whether to determine the confession was unduly coerced. But odds are it’s just a written report of the session results, not a video of the entire exchange. (I always love the _Law & Order_ technique where they weasel around the fact that the cops can’t promise anything specific by saying “it will go harder on you…” or “Confessing will make things go easier…” or “we’re just trying to help you, so help us understand…”) ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [September 3, 2022, 10:41pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/134 "2022-09-03T22:41:31Z")
> [@Dr\_Paprika](#): > > (1) Pretty sure hours are longer on Saturn. Yeah, I think you are mistaken, depending on where you are “on” Saturn. If you measure an hour as one-twenty-fourth of a day, Saturn completes a rotation in under 11 of our hours, so a Saturnian hour would be less than half of one of our hours. Alternately, if you are relying on GR time dilation due to the difference in gravity, my weak mind is telling me that any place that could realistically be described as “on” Saturn would still record shorter hours on an Earth-made watch, if its movement could be observed from here, the home of the hour. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [September 3, 2022, 10:44pm UTC](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764/135 "2022-09-03T22:44:55Z")
Could be. [Previous page](https://boards.straightdope.com/t/why-is-lie-detector-technology-not-considered-viable-in-a-usa-court-of-law/968764.md?page=6)