ELI5 Lie Detector Tests - how do polygraph tests work?

How does a lie detector test work? If people don’t trust their accuracy, why do agencies like the FBI and CIA still use polygraph tests? How is a polygraph test actually conducted? Are there any proven methods or techniques to "beat" a polygraph test? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: amainterrogator, rhomboidus, slightydamp_clothes, jetscootr, happy_bridge, baliflipper,jarljam and antechronos To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]