Sneak

Sneak is a Fallout, Fallout 2, Fallout Tactics, and Fallout 3 skill.

Quiet movement, and the ability to remain unnoticed. If successful, you will be much harder to locate. You cannot run and sneak at the same time unless you have the Silent Running perk.

Fallout, Fallout 2 and Fallout Tactics
Initial Level: Starting Sneak skill is equal to 25%  (1% x Agility). Average characters will have a 30% Sneak.

Fallout 3
Your stealth state is displayed when you crouch (on the PC, press L-Ctrl):
 * [HIDDEN] means nobody detects you.
 * [DETECTED] means someone sees you, but is not currently an enemy.
 * [CAUTION] means someone is searching for you.
 * [DANGER] means you have been detected by an enemy.

How stealthy you are is affected by many factors:
 * Sneak skill: Your Sneak skill only helps you when you are crouching. The higher your Sneak skill, the easier it is to remain undetected, steal an item, or pick someone’s pocket.
 * Enemy’s perception: Some enemies are less perceptive than others, and therefore less likely to detect you.
 * Line of sight: An enemy is much less likely to detect you if he can’t see you.
 * Light level: You are harder to see in darker areas, or at night, if you’re outdoors. Your Pip-Boy light also matters, so turn it off if you want to be sneaky.
 * Movement: You are hardest to detect when motionless, easiest to detect when running.
 * Apparel weight: Heavier apparel makes more noise when moving.
 * Sound: Most melee weapons make very little noise; bigger guns make a lot of noise.

Attacking while undetected gives you an automatic “sneak” critical.

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