Here's the TLDR; polygraph tests really test for stress indictators. If you think they work and you generally stress out when lieing, and you really dwell on the 'oh my gosh, they're going to know I lied, because of the test and I just lied', your stress indicators will be off the chart, and there you go.

If you know they're bunk, and so you can lie without stressing out, then they won't detect stress, especially if you've practiced with a polygraph. But, they usually do some sort of calibration. If you're calm or stressed the whole test, the results are inconclusive. You want to be calm when giving most of your answers, but stressed during the calibration questions where they expect you to be stressed.

The only reason you should submit to a polygraph if is if you want clearance in the US. Or you want to be a on a trashy talk show (eh, someone's gotta be on those, I guess). Anywhere else, stick to your guns and refuse on the basis that they're not reliable and it's a waste of everyone's time; don't be goaded into the 'well if they don't mean anything, why don't you just take it'

Of course, sometimes you might find yourself in a situation where the easiest path to what you want is through a polygraph, and it's easier for me to say don't take it, than for you to refuse.... like, do your best, I guess?

Thank you!!

I vote for a trashy talk show full of HN crowd.

The "real" TLDR (and I am not kidding here!) is that you clinch your anus during every answer. It does something to your heartrate, blood pressure, etc. that makes lies indistinguishable from the truth. Also polygraphers know this and will call you out on it if they think you are doing it. It makes all of your answers register the same and they assume that you will lie on at least one as a baseline (usually something like "have you ever told a lie in your life" or something similar).