What are some things that cops know, but most people don't?

Cross-post of a fantastic Quora answer by a guy named Tim Fry.

What are some things that cops know, but most people don’t?

That unless you broke the law, you probably have the right to just walk away (and you probably should). I teach my kids and their friends that if a cop walks up to them and starts asking them questions, the only thing that should be coming out of their mouth is, “Am I detained or am I free to go?” If they’re free to go they’re to walk away and, when out of earshot, call me immediately. If they’re detained they’re only allowed to identify themselves and demand to talk to me.

That in the majority of states you can record anyone (including police) in public, and without their permission. Likewise, when not in public you can record any interaction you’re personally involved in (in most states; check your local laws).

On a traffic stop the police have the right to order any occupant in or out of a vehicle, but you don’t have to give the police the opportunity to enter your vehicle. If an officer has “plain smell” of something he can articulate is illegal, it is an exception to the warrant requirement. If you crack your window and stick your license, registration, and insurance through that crack, the police probably can’t smell smells from inside your vehicle. The officer can then order you out of the vehicle (he doesn’t need a reason), but if the “smell” isn’t coming from your person, and you lock your car and close the door quickly behind you, the officer may never gain access to the “smells”.

When an officer says “you’re free to go” during a traffic stop, you no longer have to listen to him or cooperate with him in any way. If an officer says, “You’re free to go, but do you mind if I ask: ‘Is there anything in your vehicle that shouldn’t be there?’“, one good way to respond is, “Have a nice day officer”, and drive away.

If you lie to an officer, it could be considered anything from “obstructing and delaying him in his duties” to being an accomplice or accessory to a crime. Officers are free to lie to you with impunity.

Smoking cigarettes, using mouthwash / breath mints, or sucking on pennies neither hide the odor of alcohol on your breath, nor do they affect the intoxilyzer / alco-sensor / lifeloc instrument.