You should ALWAYS refuse a polygraph. It's bullshit that's about as accurate as aura reading or tarot cards used by cops to convince retarded criminals to confess. There's a reason they haven't been admissible in court for over 20 years.
There are actually exceptions. While in many places, they're inadmissible in all circumstances, including by the defense, some courts allow them if their admissibility is stipulated by both parties.
(There shouldn't be exceptions any more than you should be able to admit divining rod results in a case about water rights.)
What the actual... why would your employer want you to take a polygraph ?
Lots of glowies require them.
And because it's one of my favorite Mr. Show skits, I'm just posting it because fuck it.
You know the one group of people who will always “pass” these tests? Psychopaths. That’s how useful this test is.
Not 100% true but psychopaths display a lot less physical response to danger than normal people, which is what most polygraphs are testing for. One of the major problems of polygraphs is that the physiological response to being falsely accused of something can be mistaken for the physiological response to the stress most people feel when lying.
If you don't believe in the magic box, though, and can suppress your natural response to stress (beta blockers can help and so can being a psychopath), they're basically a joke.
There is definitely a possibility of way more effective lie detectors using something like an fMRI because different parts of your brain light up depending on whether you're remembering something or inventing it.
Most people who actually get good results with polygraphs, though, are just good interrogators to start with and use the magic box to scare people. It won't turn some dumb yokel into Columbo.