Hard as it is to imagine, lie detectors have been sold as children’s toys for a number of years. A simple battery-operated device clipped to your fingers and would show the conductivity of your skin. The concept — which is probably not very reliable — observers that lying causes you to imperceptibly sweat which causes a sudden increase in your skin’s conductivity. These cheap toys would have a meter and you’d note the meter deflection to determine if the subject was lying.

You can debate the amusement value of interrogating your friends, perhaps, but they were pretty common and still exist (including some that shock you if they detect you are lying). Seventeen-year-old [BuildIt] has his own modern take on this classic device using — what else? — an Arduino. You can see a video of the device below.


fvb06bzirsuey29-largeOf interest is how he used the latest version of the Arduino IDE to visualize the data graphically (see right). This is easier than interpreting a bunch of numbers scrolling by on the serial terminal or having to import the data into a spreadsheet. You can find the graph under the Tools menu listed as Serial Plotter.

You don’t need a lot of external parts for this project, although the finger clips and the cardboard box will take a little mechanical skill to complete.

We’ve looked at galvanic skin response and other biosignal processing before. You can do a lot more if you build a little more hardware.

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  1. Sorry, but…

  2. sonofthunderboanerges

    Adam Conover is always too generalisttic with his many claims on his TV show. The Polygraph is only as good as the technician operating it and analyzing the results. It’s not meant to detect lies. It was meant to detect stress during simple binary questions AFTER establishing a baseline for the target. It is only detecting deception or evasiveness to the questions. Everybody can’t do the tests only highly trained technician/analysts. There are ways like VSA and EEG/Tomography (which is much more reliable). The later one measures the different temperatures and EEG signals coming from your brain. You are shown several photographs and if you show a major difference than your baseline measurement then you are very familiar with the content of the photo. Also it depends on which part of the brain is reacting too.

  3. Nah, the polygraph is bullshit. It’s been tested. The way to pass one is to suck up to the “technician” giving the test. If he thinks you’re guilty, you fail. He might not know it, but that’s the biggest influence on his “interpretation”. They’re usually independent operators who hire their services out to gullible businesses. They’d be better off with graphology.
    Talking of graphology, is that why some places want hand written application letters? There’s a ton of money in selling nonsense to businessmen, apparently. If I had no shame I’d make a fortune doing it.
    As it is, I’ll probably just modify this design slightly and start a bogus religion. Everyone knows that’s where the real money is.

  4. sonofthunderboanerges

    Greenaum – Well I guess you are correct if the PG box was in the wrong hands like amateurs of local police departments. However, a Certain Important Agency in USA uses the “box” to screen new employees and existing employees every 5-years just to keep them honest. When I say “stress” I mean your body exhibits galvanic skin conductance, change in respiration, and your heart beat changes when your under stress and body loaded up with coritsol and adrenaline. The box detects these abnormalities when after baseline is established with control questions. The operator watches these 3-4 conditions on a graph. He/she marks off where “changes” occurs during binary YES or NO questions are asked.
    The operator must be trained in how to interpret the readings. As just any local yokel cop is not that skilled. Some times a person with a psychology degree is required. So yes its granted that in MOST scenarios the bog is bogus. But when used by skilled professionals who’s job is to root out liars, it’s very effective.
    Imagine every 5-years your company employer makes you take one of these probing tests. You wouldn’t be able to hide anything – not even your seemingly innocent alternative lifestyle. That may explain why this particular US federal agency above has a very high turnover in employment and then they go out and write a book.
    Yes you can BEAT the box. But you need to be trained on how to do it. You could bribe the operator but that will only last for so long as he/she is also tested every 5-years. And when things start going sideways at the company they up the period to once every year to make things much more interesting.
    I like graphology, I use it a lot. I also like body language. You don’t depend on these things. You just use them to give you a clue what your dealing with initially. Then you use the OTHER data to fill in the blanks later.
    I know I’m preaching to the choir…

  5. it has been proven to be bullshit no matter which company or outfit runs them, the basic concept is bullshit and will always be, it is too general and based around unknown factors, that “stress” you are talking aboput is so general it hurts how anyone could think it useful for anything.

  6. When I saw the headline, I thought this would be an accessory for the Galaxy Note 7.

  7. TacticalNinja

    Yes, because LED’s are more fascinating to watch than your leg getting a 3rd-degree burn.

  8. How simple could you get on a device like that to warn you that phone or tablet was overheating?
    I’m thinking something no more than 2mm thick, no more than about 40x60mm large, and you can just stick on the back of it. Do you think it’s doable with some combo of a peltier (used as thermoelectric voltage source) element and the guts from a musical birthday card?

  9. Peltiers need a cold side, they work on the temperature difference between sides. In a pocket isn’t a good place for that. They’re pretty crap at generating power anyway.
    Simpler would just be a thermistor and a little battery, or power it off USB. That said, phones have internal temperature measuring. Maybe an app could monitor that, in the few seconds you have before the power goes out and your leg catches fire.

  10. notarealemail

    Polygraphy is pseudoscience.

  11. sonofthunderboanerges

    notarealemail – Yes when administered by amateurs. And I think it doesn’t work on psychopaths either (snicker)

  12. no proven to be pseudoscience always, there are several factors that mean far more than any “stress” measured

  13. And Scientologists call these e-Meters which have fantastic powers!

  14. sonofthunderboanerges

    Galvanic skin response is NOT a lie detector (per se). It MAY be indicative of ‘stress’. Sometimes people sweat more when lying but not always. There are many indicators of emotional stress when trying to be deceptive. like dry mouth, eye shifting, eye gaze direction, vocal anomalies, changes in respiration, etc. A more reliable method is the VSA method which remotely tracks stress via your vocal anomalies. The Israelis perfected the VSA device (for purchase) called TRUSTER. If somehow HaD could reverse-engineer that and have an Arduino operate it that would be very cool. No need for human contact, just a microphone as your sensor, Imagine how it could be used in our 2016 American presidential election by just aiming it at the TV speaker and watch the display go off the chart on one particular candidate who is especially truth-challenged.

  15. Dante Roumega

    I 100 percent agree with you thats why when i made this video I did my best to explain that this only a tiny fraction of the test you could do and isnt 100 percent accurate but thanks for providing more information I might make another one with even more sensors like a microphone to try and make it a little bit more accurate

  16. sonofthunderboanerges

    Dante Roumega – Very cool!
    However, before doing the microphone thing please do exhaustive research on Voice Stress Analysis via Google and Wikipedia. It is NOT a simple thing and is kinda’ complex. It involves detecting the LACK of subsonic signals from your throat called micro-tremors. Evidently, the TRUSTER people made a complete science of analyzing different kinds of anti-micro-tremors to identify all sorts of stress reactions of the human throat. TRUSTER can detect evasiveness, deception, and all sorts of emotions just from listening to people talk. You can use it on the phone, video, radio, or live TV. https://en.wikipedia.org/wiki/Voice_stress_analysis
    Do NOT download the so-called FREE TRUSTER on YouTube. It is a TH virus.The real one costs $195 USD. However, you can get a small hardware version cheaply on EBAY or AMAZON.
    FYI – No such thing as a electronic LIE DETECTOR. Polygraphs can only detect stress while being asked simple binary questions.It is the Polygraphers job to analyze the results to determine deception or evasiveness. It is a science or trade-craft, not a parlor trick.Some people know how to “beat the box”, however, that is also a trained trade-craft.

  17. Polygraphs don’t even measure “stress”, whatever set of objective criteria “stress” is supposed to be. The correlations they’re based on don’t exist. It’s all voodoo and confidence trickery. Faith.

  18. Dante Roumega

    Awesome article!

  19. My latest project has taken to this method only it polls for calibration of the suspect then polls variation from that, rather than a set total as seen in the above’s Arduino code. Then once it decides on guilt or truth, well… https://hackaday.io/project/14813-arduino-water-boarding

  20. sonofthunderboanerges

    rellimvt – You need to watch the movie ZERO DARK THIRTY (2012) – there is a number of aspects the benighted people of the world don’t understand about EIT (enhanced interrogation techniques) i.e. “water boarding”, that are just totally ineffective at arriving at the “truth” of a situation. Yes you could automate it but the results would be the same. It might work on a street thug who is hiding the money he stole yesterday but it is a total waste of time on a trained psychopath with pre-concieved pseudo-back stories built-into his head by his handlers. Only intellectual giants like Donald J. Trump think they work ALL the time for ALL detainees. Try automating a voice stress analysis program and then you’ll have something…

  21. My pants are on fire
    a burning shit
    (on the melody of “Love Is On Fire” from Italobrothers)
    I just saw you can buy fire retardant underwear for motor sports.

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