Anyone know how the police hiring-process polygraph test works?

I'm far from an expert in this regard, but I have seen a few documentaries about polygraphs and their bogus results. My understanding is it's very common for a lie detector to say someone telling the truth is lying as a polygraph really measures nervousness, and takes any signs of nervousness like increased heart rate as a sign of deception. Maybe someone panics because they're worried they're going to get caught, maybe they panic because someone just asked them about being a pedo which scares the crap out of them. It's less common to get truthful results when someone is lying, unless of course they use one of the relatively simple ways to beat a lie detector like clenching your anal sphincter (yes, you read that right... watch the Penn & Teller episode of Bullshit! on lie detectors and you'll know how that works) Most courts won't accept polygraph results as evidence as they are notoriously unreliable, so I don't think they could press charges with a failed polygraph alone. But I don't see why they couldn't investigate something further if it really bothered them (i.e. failing a questions "are you a serial killer"), but if its minor ("i.e. do you smoke weed?") I doubt they'd care too much. Half the value of the polygraph is its ability to make people blurt out dumb stuff they shouldn't. They'll give you the test, make you feel nervous by giving you absolutely zero feedback on how you've done, and then after the test is over and they disconnect everything, before they talk results with you, they ask you "Is there anything you want to tell me before I go over your results?" hoping you'll blurt out a confession. Again, check out the Penn & Teller Bullshit! episode on polygraphs, plus I'm sure there are a ton of videos out there showing how these really function and how they can be manipulated. EDIT: It is possible to try and beat the lie detector test with all kinds of tricks from taking certain drugs in advance, to clenching your bum, to broken glass in the shoe, etc. but if you do get caught doing that, I'm pretty sure that would disqualify you right there. Somehow I doubt that someone with only a few bad decisions here and there in the past would be disqualified from becoming a cop.

This ^ ^ ^ ^ ^ ^ ^ ^ Or the test administrator will look over the results, act puzzled, say he didn't get a good read, and ask you a few of the same questions over again. It's a voodoo science junk box, used to intimidate you into reneging on your answers or blurting out 'the truth'. It often doesn't matter as much what the truth is, merely that you tried to lie and cover it up.

Hypothetically, if they are going to poly you, they are also going to have your entire criminal history.

Hypothetically, if you had a lapse of judgment several years ago, which was later expunged from your record . . . you will have to check your state law to see how much expunging really does.

The poly is really about the administrator, not about the machine.

To answer your other question, it depends. For fed jobs that require a poly, you'll sign something on your clearance paperwork that says the things you admit to will not be held against you criminally. E.g. they want you to be honest so you don't have secrets that can be used to blackmail you. There is a website somewhere that shows the type of shit people admit to, get rejected, appeal, and get their TS anyway.

So, you stole a car, right?

if they know what they are doing, you won't beat the machine. trust me.

but here is the thing, what they want is to make sure that you tell them the truth. so lets say you used some weed in the past. tell them about it. if you raped and killed 23 tourists, don't apply to the cops. stealing a car falls somewhere in the middle.

+1 Good administrators are worth their weight in gold and can pretty much interpret you answers with amazing accuracy

So you're asking if they(the LE Agency) asks: Did you commit any Undetected Felonies"??

My agency asked that question in a Variety of ways...Just say no and Believe your own lies...

Agree with what Globe said. Your best option is to tell the truth. Any answers you provided on your employment paperwork with the police dept will probably be asked again on the poly. Don't change your answers and dont lie. The poly is nothing more than a tool used by the interviewer. For people properly trained to use them, they are an invaluable tool and you will not beat them.