How do you know you are out?

Simply being hit by a paintball is not enough, conditions apply.
A paintball has to hit you and break.

A ball that bounces off you does not count unless you call yourself out before you check. This creates confusion and can lead to people throwing large inanimate objects at you.
A Paintball that hits an object and 'splatters' on you do not count.

A shot on the gun does not count. Quite simply, any pellet that hits your body and breaks is a hit and you are out.

 Some players prefer not to let head, arm and leg shots count.