Defeating A Lie Detector

I notice more and more of these talk shows have shows that use lie detectors on them.

My question is does anyone know of a way to defeat them. I don’t necesssarily mean being able to lie and have it show true, but just being able to lie and have the results be “well we can’t tell either way”

IIRC I read somewhere where you could put a thumbtack by your big toe and everytime you answer a question you step on it. That way it’ll make the result inconclusive.

It’s not particularly difficult to fool a lie detector because it’s not the machine that’s detecting lies – it’s the operator of the machine that’s interpreting its readings as lies. If the operator is lackadasical (and I suspect you’ll get more talk show work if you don’t look at things too closely), lies that are obvious to other operators will be ignored.

The thumbtack trick can work, since the detector measures the various physiological components of stress – the more stress, the more likely you’re lying. However, the best way to fool the test is to use the thumbtack when the operator asks the baseline questions (i.e., those in the beginning like “Is your name, Joe Smith?” that are used to determing normal parameters). If there’s a lot of stress in the answers to to these, you can lie like a rug and the stress will be less than normal. A good operator can tell what’s going on, but others may be not be willing to question things.

I don’t know how to go about beating them, but I had always assumed that the greater the testee’s (Ha!) intelliegence, the better chance they had at getting over on the interpreter. However, one of my psychology professors claimed the opposite was true - it’s easier for dumb folks to lie and get away with it. My belief is that dumb people are less spt to be tested, as they would probably tell dumber, more obvious lies to begin with.

oops, less “apt”

Supposedly, with training and practice, one can also gain some control over the supposedly involuntary reactions that are measured, which include heart rate and moisture levels in the finger tips.

Some CIA employees are said to be trained in this art, for the purposes of defeating lie detector tests administered by “the enemy,” but it seems to have now become somewhat common knowledge within the Company. Aldrich Ames didn’t exactly fail that lie detector test, but he didn’t entirely pass it either. That gave him enough time to compromise still more operatives than he would have had he set off the red lights.

To throw in a substanceless rumor, someone once told me that dehydrating oneself for a day or two before the test can throw off the fingertip test. Seems to me like that might actually work against you: if you’re dehydrated, you might only trigger the sensors when you’re lying, which could actually give a more accurate picture rather than an obscured one.

I used to work for a jewelery store and they periodically made all the employees take these tests.

Almost every time I took one, I lied and was never questioned. One time I didn’t lie and the guy giving the test said I was not being truthful…go figure.

I wasn’t a thief, I just lied about things that I felt was none of their business…Casual drug use and other past indiscretions.

Inicidentally (or not) there was a report in the New York Times recently on the findings of some researchers who tested people of various trades and professions for how observant of lies they are.

They found that the only people who could tell the difference between when the test givers lied and told the truth were CIA agents.

All the other people from all the other professions were so inaccurate, they were merely guessing.

I don’t know who first said “everyone’s a critic,” but I think it’s a really stupid saying.

I just read a newspaper (magazine?) article questioning the reliability of these devices. The technique they mentioned to fool one was, as posted previously, to create some sort of bodily reaction to all questions in order to make the comparisons inconclusive. They specifically mentioned biting your cheek or “tightening the anal sphincter”.

Whatever works.

“non sunt multiplicanda entia praeter necessitatem”
– William of Ockham

I strongly suspect that the polygraph is junk science.

I have no hard facts at my disposal, but there’s a lot of documentation that liars beat it, and truth-tellers failed.

It speaks volumes that the courts will not admit polygraph evidence.

If you’re an optimist, you haven’t been paying attention.

A simple search in the web found this interesting testimonial and explanation of Polygraph tests:

And, of course, an exposition against the test:

One way to beat a lie detector test is some method acting. Basically, decide what is your reality before you start (i.e. never done drugs in my life) Then believe that for the duration of the test.

For most people the best way to “beat” it is to just not admit to anything. Here is my personal experience.

Many years ago, my work would do random lie detector tests. It was a large national chain, and in the five years I was there, they only came to our store once. All management was tested, so I got the honor of seeing it first hand.

In my opinion the lie detector was more of a prop than anything else. They bring you to an office, strap you in, and let you sit there a while. Then they came in and explained the serious consequences that could happen if you were not being truthful. They even said they would rather help people than get them in trouble, so if there was anything you wanted to “explain” first now was the time.

Then the test. I knew I didn’t do anything wrong, so I wasn’t concerned. They asked the expected questions, and I answered them truthfully. When the tester was finished he said there were a few responses that he was “concerned” about. He wanted me to take a few minutes to think about my answers, and left the room. When he came back, he again gave me the chance to “come clean.” Then he asked the most incriminating (sp?) questions again… another chance to confess… then it was over. I passed and kept my job.

Others however didn’t do as well. There was a group of warehouse workers who admitted to smoking a joint with a truck driver. There were five people involved including their manager. Four admitted to doing it (same tactic as was used on me), but the manager continued to deny it even when directly confronted. Four were fired (actually resigned to avoid “prosecution”)… the manager was not, because he knew that the results would not stand up in court against him, and the company wasn’t really willing to go that far.

Manny long years ago, as a psychology student, I was an assistant to a researcher studying polygraph results. Zyada’s got it right when she says “method acting” is one way to beat it. As a general proposition, if you believe, or can rationalize, that the answer you are giving is true, odds are that the polygraph will not detect it as a lie. My roommate at the time was able to beat the test this way.

Rumor around the lab was that if you sprayed hair spray on your hands before the electrodes were hooked up it would impede the sensitivity of the monitor and thus the effectiveness of the test. We always had our subjects wash their hands before participating in polygraph experiments.


See “The Deciever” with Tim Roth and Chris Penn. Good movie.

Psych 101:

If you believe the graph can be fooled, you’ll likely fool it.

It was the people who believed that the graph would actually detect lies that were accurately caught, because they did have stress when they lied because they believed that the questioner could see that they were lying.


The operator has some data on you and any relevant events. Thus (s)he forms, out front, an opinion of your “guilt” or whatever. Unless you are extra expressive in the monitored bodily parameters, that’s the main part of the game.

The one time I went before such a test, I was not given any intimidating lecture. Then, on my request, the operator allowed me to provide him with a list of questions related to me that he could ask me in a new test. He did very poorly in discriminating between my truths and my lies. Of course, he had all kinds of excuses as to why. Of course, the questions I gave him did not center on any issue, and he had no time to mull them over in order to accrue any personal opinion on what the true answer to them might be in my case. Not a real test of polygraph testing, but an indication.

Ray (Did this really happen or am I lying?)

What the hell happened to the voice stress analyzer that was supposed to be so much more accurate than the polygraph?

Designated Optional Signature at Bottom of Post

To fool the machine is pretty easy but the actual decision is made by the operator.

Whenever you give a truthful answer, just add a little ‘ummmmm’ before the answer, with the right emotional inflection, youll have it done.

There is a personal PC program, Truster, whereyou can use your PC as a lie detector, with a microphone.

BTW, the aformentioned (by me) magazine article was in this month’s Scientific American if anyone’s interested.

“non sunt multiplicanda entia praeter necessitatem”
– William of Ockham