The experience bar shows how visible you are to zombies. Based on how you move, this bar will grow and shrink, giving you a visual indicator. With time, players will learn how close they can't get to zombies without garnering their attention. - Official minez.net site
The following chart details your visibility on a scale of 0 to 18 depending on your current action.
|3.1||Standing still while crouching|
It has been stated that rain and nightfall decrease your visibility. The precise amount has yet to be researched.
It has also been stated that PvP will cause zombies to investigate. So think twice before attacking someone.
Possible Ideas for Page Content Edit
Precise range of visibility for zombies according to aforementioned actions, tips on sneaking around zombies (Different page?), ???