re: Polygraph test?

Not easy to actually beat, but easy enough to render any results useless once you understand what and how the data points are being measured.

For example most people can lower or elevate their heart rate a bit by simply willing it, effectively altering blood pressure by detectable levels. Respiration can be manipulated both by rate and and speed.

Cops have used it as an exclusionary tool, but more often as mentioned, a scare tactic.

We got to 'play' with them a bit in the military as an MP, by play i mean to assist investigators training to try to spot deceptive answers, or attempts to beat/invalidate the results.

If you want to play with them, for a couple hundred you can get a 'USB polygraph' that plugs into a laptop or whatever. I think even Amazon has them now.