Is that entirely true? I would imagine that unless they have some very very well trained hypnotists, it would be very difficult to make people tell the truth. Of course, it's all suggestion, so in theory it's possible - but don't you have to be willing to be hypnotised..
Hmm apparently they use these: http://en.wikipedia.org/wiki/E-meter
Seems a bit too much like a Ghostbuster machine if you ask me