Lie detectors in court

[sair5412]

Why don't courts use lie detectors in court? Not as the main evidence but as a back-up kind of thing.

Has it ever happened in a court?

[dzug]

Because they don't work, or rather they don't detect lies, they detect nervousness.

[badboy4life]

I fooled a "lie detector" 100% for my psychology degree

[Loosehead]

The trouble is that they are unreliable and a jury could be misled by their own opinions of lie detectors. For example if someone denies something and it the detector says they are not lieing the seeds of doubt are sown, similarly if the detector says they are lying. I think both prosection and defence have good reasons for not wanting lie detectors.