> considered valid evidence They're considered a valid tool for coercion. Stupid criminals who watch too much TV think they work and some cop comes in and say

> considered valid evidence They're considered a valid tool for coercion. Stupid criminals who watch too much TV think they work and some cop comes in and says he failed a lie detector test and they confess. In that way they actually do work. Assuming all you want is a confession but if the person actually provides evidence of their own guilt they so be it.