27th June 2009, 8:29 PM
Yeah but I tore one a part for fun and apparently when reading the output of one, they can tell nervousness from lying. If you are too nervous, they schedule it another time because it will interfere with the readouts. It's not just a simple quickening of the pulse, it's also irregularities and change that are only associated with the act of of lying. It's not perfect, but it does offer pretty valuable information.