lie detector guide

When somebody lies, their body gives several clues and signals. We’re typically told to look for signs like unusually nervous behaviour. If people are lying, they might stammer more than usual, might look down at the floor or could be twitchy and fidget more frequently. Even with these clues, it can be hard to tell if someone’s lying or telling the truth.

Lie detector tests can be used to find out if someone is lying. So, what is a lie detector and how exactly do they work?

What is a lie detector?

A lie detector is a test that’s used to discover if somebody’s lying. It typically picks up on the body’s subtle signals, more accurately than you might notice them on your own.

What are common kinds of lie detector?

There are several different types of lie detector. Some are more popular or more widely used than others.


Perhaps the most well-known of all lie detectors, the polygraph is commonly known as the ‘lie detector test’. This method measures things like pulse, blood pressure and breathing to look for signs of nervous behaviour.

When you’re lying, your body gets defensive and starts a ‘fight or flight’ response. You might breathe more quickly and your heart starts to race. These physical signs can be detected using a polygraph test. Though these tests are the most commonly used, they’re not necessarily reliable. Often, people get nervous just being asked questions even if they’re telling the truth.

Voice Lie Detector

The voice lie detector looks for changes in someone’s tone of voice. When someone is lying or feeling ashamed or guilty, their tone of voice naturally lowers. Liars might also pause more when speaking, suddenly stop talking to avoid incrimination or might accidentally give two different stories. All these features can be checked with a voice-based lie detector.


The EyeDetect® test is described as a ‘next generation lie detector’. Instead of using your heart rate and breathing, this test works by noticing subtle eye changes. Lying can change your pupil diameter, blink frequency and where you focus. All these things can be measured using the EyeDetect® test.

The EyeDetect® test is administered using a computer. This makes participants less nervous than if they’re being asked questions by someone else, so there are less likely to be false positives and the test will be more positive.

When can a lie detector be useful?

Lie detectors were a long-term feature of the Jeremy Kyle show, intended to find out if people had lied to their friends and if partners were cheating, but lie detector tests aren’t just useful for dramatic daytime TV.

Lie detectors can also be useful, alongside other tools, for legal purposes and job interviews. Our private investigators can use lie detector tests to find out when someone’s telling the truth and when their story is made up. Lie detector tests can be used to find out if people have been drinking or taking drugs, if they are telling the truth in a job interview or if they’re lying about where they were when a crime was taking place.

If you’d like to know more about how we can help you find the truth, why not call today to speak to one of our Preston-based private investigators? Call now on 01772 334 700.

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