Nothing But The Truth: Lie Detection

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SWBAT explain how lie detectors operate, build their own lie detector and explore how body language and heart rate reveals if subjects are telling the truth.

Big Idea

It's no surprise that criminals often choose to lie to police. Learn how investigators use science to tell a lie from the truth.


30 minutes

We start this lesson a little differently than the others in the unit. Instead of a Forensics challenge, I introduce and have the students play the classic icebreaker, Two Truths and a Lie. In this game, students write down three facts about themselves, one of which id made up. We go around the class, having each student read their statements, then trying to determine which one was not actually true.

After playing, I ask the students to consider how they fet they knew which statement was false. Students will provide suggestions, such as how one statement sounded too strange to be true, how the person smiled when they read the false statement, etc. I list these ideas on the board as students provide them.

Before the lesson began, I posted the three videos below on my website. Once the game is finished, I direct the students to the videos and provide them about 15 minutes to watch  1-2 videos of their choosing. I direct them to write down any information that tells them how to determine if a person is lying, as they watch.

How to Detect A Lie

Human Lie Detector


8 Ways to Spot a Liar


After watching, I ask random students to add to the list I have stared on the board based on the information they got from the videos. I call on them individually to provide additional "tell-tale" signs of lying.


15 minutes

Once we list the possible signs of untruth, I pass out one page from the Lie Detector Article to each student. I have them read the page silently, then sit with the students who read the same page as themselves. They reread with their group, stopping after each paragraph to discuss and highlight key information from that section.

Once everyone has read and discussed their page as a group, we "Jigsaw", and regroup the students into groups of 4, each one having read a different page. Each student will summarize their page and explain the key information to their counterparts.  Then, the group will work together to create a one paragraph summary of the entire article, using at least two pieces of evidence from the text to support their thinking.


Do you want to make PDF files from the web just like mine? Watch this video to learn how!


10 minutes

Each group now shares their summary with the class, making sure to cite at least one piece of evidence from the article to support their ideas. Each group selects one presenter, who reads their summary aloud.


30 minutes

Now that students know a little more about the signs of lying and how lie detectors work, they get a chance to build their own simple "lie detector" and observe biological factors to determine lie from truth.

I pass out the Lie Detection Lab and read through the directions with students. Once students have read through the directions, I allow them to select a partner and to begin conducing the lab.

Note: There are a few skills that students will need prior to beginning this lab, which may require some front-loading on your part. for more information, please see my reflection.

The end of the lab requires students to create a chart or graph to analyze and demonstrate their accuracy in lie detection. While they are analyzing their results, I encourage students to conduct a little research into how to pass a lie detector test to determine if the test subject could have done something to skew the results.

Once all students are finished, I have them present their chart/graph to the class, discussing their results and describing what factors may have had a part in these results. (Reading the blood pressure monitor incorrectly, miscounting heart rate, etc.)


15 minutes

While the chart/graph that students have created serve as a good assessment of their understanding, I also like to provide a more fun way to assess what students have learned. To do this, we watch excerpts from the game show, "Would I Lie To You?", in which people listen to ridiculous stories and have to determine whether or not the storyteller is telling the truth.

As we listen to each story, the students take notes and try to determine on their own whether or not each story is true. With each story, I ask random students to explain why they thought they way they did, using their observations as evidence.