There are many lie detectors on the market but it's extremely difficult to find a free one. You will likely find several free trial versions online, but there is only one complete test that is actually free. The software is called Prevaricator and it uses voice stress analysis (VSA) to detect lies. The lie detector test itself is free, but you will need a microphone hooked up to your computer to use it. Even with the best computer microphone money can buy, it's still difficult to get a truly accurate reading from a VSA lie detector test.
Go to www.LieDetectionSoftware.zoomshare.com and scroll down the screen. You will see a link that says "Click Here to Download." This link will allow you to download Prevaricator.
Click on Download and then Save. Save the file with whatever name you want to save it as.
Open the software on your computer.
Talk through your microphone about whatever you choose. When you're done talking, click on the playback button. The lie detection software will play back your recording and graph out your voice on a virtual polygraph screen. When you lie, the audio marks will enter the red border on the top and bottom of the graph. When you tell the truth, the audio marks will stay in the middle of the graph.
All lie detector tests on your computer will use VSA. This means they won't be the most accurate form of lie detection. There are too many factors, like ambient sound in the room or a sore throat, that can throw the lie detector off, and skilled liars will probably beat VSA. With that said, you won't find any very good lie detector tests for free.
Even if you buy a $1,000 lie detector test that uses VSA, you will have to have a quality microphone and a soundproof room.