[TDL]

It is an approved technology by the US government. It is mostly used as an interrogation tool as opposed to a lie detector. Having only worked with interrogators I only know second hand how it is used, from my understanding it usually used in a good cop/bad cop scenario (such as, "The machine is saying you are lying, let me help you out and tell me what happened.") I am sure there much more knowledgeable people then myself on this forum. Short answer: as a lie detector it is unreliable,but as a interrogation tool fairly effective.

[mtrimpe]

From what I've understood polygraphs aren't actually lie detectors but 'emotional distress' detectors.

That means you don't know whether what's being said is true or not, but you do know when you've found something worth digging deeper into...

[TDL]

Pretty much. They've been sold as lie detectors based on the notion that stress == lies, this is obviously incorrect. The same notion is also what make voice stress analysis unreliable as well.

[wisty]

They work especially well if people think they work.