How do you build a lie detector?

Answer 1

Most lie detectors are based on detecting the activation of the autonomous nervous system when lying. Such effect are increased sweating and elevated blood pressure.

A blood pressure meter could thus be used as a primitive lie detector. This method would however require information on changes in person's blood pressure while lying and would still be prone to confounding factors such as stress.

Answer 2

It is possible to make one but no one uses the materials needed in a regular home. Because you can only get the parts in a build-it-yourself kit.

Answer 3

You can find a step by step guide on how to make lie detector on instructables.com/id/Make-a-portable-handy-lie-detector-in-Altoid-tin/