We’ve all been in a similar situation in the past. Mom walks into the kitchen and finds evidence of unauthorized snacking. The inevitable questions come. “Who did this?” “Was it you?”

If you’re the guilty one, you have two options: tell the truth and face the consequences or try to tell a convincing lie to avoid the consequences. We urge you to tell the truth, because lying isn’t a good habit to develop. Besides, most parents have a built-in sense that tells them when you’re not being truthful!

Law enforcement professionals, such as the police, often need to know when someone is telling the truth or not. Since they can’t rely on parental instincts, they sometimes turn to a special tool called a polygraph machine.

A polygraph machine is more commonly known as a “lie detector.” You’ve probably seen polygraph machines used in movies or television shows. You may have wondered whether they can really determine when someone is lying.

Polygraph machines measure certain bodily functions, including skin conductivity, heart rate, blood pressure and breathing. These are functions that can’t be easily controlled by the mind. Many people believe measuring these functions can reveal when a person is not telling the truth.

A polygraph test usually involves asking a person hooked up to a polygraph machine a series of questions. Some questions are control questions. These are simple questions with known answers, such as the person’s name and address.

A baseline reading is established based upon the control questions, since the examiner will know the answers are truthful. When the key questions — questions the examiner doesn’t already know the answers to — are asked later, the responses can be compared to the answers to the control questions.

If the functions being measured differ from the measurements taken in response to the control questions, the examiner will likely conclude that the person being tested isn’t being honest. But how reliable are these tests?

Critics of polygraph machines believe that they aren’t reliable, because there are too many variables involved to be a valid scientific test. Many courts agree with the critics. Polygraph results are often not admissible in court proceedings. In areas that do allow polygraph results, they are often only allowed to be used in limited ways and not as proof that someone is lying.

Researchers have found that polygraph machines may detect lies in many cases, but that they may be susceptible to errors, too. For example, some people have shown that they can use certain strategies and techniques — called countermeasures — to fool polygraph machines.

So could you beat a lie detector? Maybe! Common countermeasures include trying to increase physical responses during the control questions. This could take the form of purposefully increasing your breathing rate or pinching yourself. The idea behind these types of countermeasures is to establish a false baseline on the control questions.

Others claim they can beat a polygraph machine simply be getting a good night’s sleep and remaining calm throughout the examination. Some people mentally repeat the control questions to themselves as they answer the “real” questions. Doing so may help to control their bodies’ involuntary reactions.

27 Join the Discussion

1 Star2 Stars3 Stars4 Stars5 Stars  (31 votes, avg. 4.06 out of 5)
  1. I was wrong. But today’s was kind of fun. I’ve beaten it before a lot of times. Now the only thing they’re missing is a desk in a dark room with a bright lamp…
    I think tomorrow’s WONDER will either be about Medusa or the Minotaur. Go Greek Mythology!!!


    • You were SUPER close to guessing our lie detector Wonder– good try, Emily! We LOVE your suggestion of the desk and bring lamp to suggest an interrogation– sometimes lie detectors are used as a part of questioning. We are so glad to have great Wonder Friends like you! :) Have a WONDERful day! :)

  2. A lie detector, oh come on, it’s the classics to beat a lie detector. You said that it measures certain bodily functions, including skin conductivity, heart rate, blood pressure and breathing. Right, because if you stay calm than you did it. :-P

    • You did a SUPER job of noting what goes into detecting lies, Carlos. We Wonder if you have been doing more research on your own? :) We hope you have a WONDERful day and can’t wait to Wonder with you again! :)

    • We are sorry to hear that you could not enjoy our lie detector Wonder video, Carley. If you’re trying to view the Wonders at school, we want to let you know that some schools/school districts put “blocks” on certain videos that come from places like YouTube or Vimeo. Because the videos we choose to go along with each of our Wonders are “borrowed” from many different places around the internet, like YouTube and Vimeo, it might be a “block” from your school or district that is keeping you from seeing the Wonder video. You might want to check with your teacher or librarian to see about getting the block removed! :)

  3. I think that telling the truth is the best way to go because although you may have to face consequences you will have to face more if you lie and your parents find out which usually they do! Just tell the truth in the first place so then you won’t be guilty or worse proven guilty!!

    • We certainly agree with your advice, Grace! Honesty is the best policy and telling the truth is the right thing to do. Also, no one likes to feel guilty– you make some STELLAR points! We are THRILLED that you’ve joined us in Wondering– we love your SUPER imagination! Thanks for commenting! :)

    • Howdy, H.i sc0re! We are so glad you found our lie detector Wonder interesting! Sometimes technology can be confusing, especially if you haven’t had the opportunity to use it yourself! We hope you have had fun learning about this particular technology and what it is used for– take a look at the rest of the Wonder when you have some time! :)

    • We’re glad you’re WONDERing with us today, MoonPie-4! We sure hope that you’ll be honest if you ever have to take a lie detector test, but it’s cool to learn about how the device works!! Thanks for stopping by Wonderopolis today! :)

    • WOW, it sounds like you had a lie detector experience of your own, Wonder Friend Guner! Thanks for telling us about the details of taking the lie detector! We are so interested to hear about it! Thanks for sharing your comment! :)

  4. :) AMAZING! I loved that video because even I know you could fool a lie detector I wouldn’t because I was taught to not lie and be honest! My mom told me I was a very honest young man thank you for the video I will post on tomorrow’s wonder.

    • Great question, Wonder Friend Brielle! Lie detectors measure lots of things, but many scientists believe the polygraph is not a fool-proof tool to use when questioning someone. The test does not matter what is said, but rather how the person speaking reacts. :)

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Have you ever wondered…

  • Can you fool a lie detector?
  • What is a polygraph machine?
  • How reliable are polygraph results?

Wonder Gallery

Try It Out

Want to know the best, most foolproof way to beat a lie detector? Tell the truth! Yes, it’s that simple. Just tell the truth.

Most kids learn from an early age that lying is not a good habit to develop. Lying prevents people from trusting you and becomes a barrier to meaningful friendships. Instead of lying, work hard to develop the habit of telling the truth. It will set you free!

And you can get started right now. Grab a pencil and paper and make a list. Think of a person who means a lot to you. It could be a teacher, a friend or a family member. Then make a list of 10 true statements about that person. These things should be statements that describe or demonstrate why the person is important to you.

When you’re finished, share your list with your chosen person. You might be surprised at the effect your list of 10 truths has. In addition to practicing telling the truth, you’ll also get a lesson in the power of words to build a person up and make them feel valued.

Still Wondering

In Science NetLinks’ Lying lesson, children learn about many different aspects of lying — what it is, why we do it and how we do it.

Wonder What’s Next?

Watch out! Tomorrow’s Wonder of the Day takes a closer look at a mythical monster!

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