Sneak

Sneak is a Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, Fallout Tactics, Van Buren, J.E. Sawyer's Fallout Role-Playing Game and Lionheart skill.

Fallout, Fallout 2 and Fallout Tactics

 * $$\text{Initial level}\%=25+\text{Agility}$$

Example: A starting Agility of 5.
 * $$25+5=30\%$$

Sneak only covers sneaking as such, while pickpocketing is covered by the Steal skill. In Fallout and Fallout 2, one cannot run and sneak at the same time unless you have the Silent Running perk.

Fallout 3

 * $$\text{Initial level}=2+(2\times\text{Agility})+\left\lceil\frac{\text{Luck}}{2}\right\rceil$$

Example: A starting Agility of 5 and Luck of 5.
 * $$2+(2\times5)+\left\lceil\frac{5}{2}\right\rceil=15$$

Sneaking may be one of the most important skills in Fallout 3 for certain characters. Sneaking up on a target allows the player character to get closer, allowing them to avoid taking damage for the longest time possible, and maximizing the damage potential through the use of "sneak-attacks". Sneaking increases the chance to loot and steal, and allows the ability to avoid some undesired confrontations, thus working as an offensive and defensive skill.

Unlike its predecessors, in Fallout 3 a player can both sneak and run at the same time (i.e. move faster while crouching) regardless of perks. However, without the Silent Running perk, the player will suffer a detection penalty while running.

Sneak states
The sneaking state is displayed while crouching, and alerts the player to detection and possible detection.
 * [HIDDEN] means you're undetected. In this state, attacking a target guarantees the sneak attack critical bonus, pickpocketing is available, and it is safe to steal, lockpick, or otherwise access "owned" property.
 * [DETECTED] means you've been detected by one or more friendly targets. Pickpocketing is enabled, but almost always fails. Attempting to steal, lockpick, or otherwise access "owned" property will fail, and may result in friendlies turning hostile or confiscating stolen goods. Sometimes an unfriendly target will see you and this will be shown instead of [CAUTION], because they haven't identified you as hostile or a target.
 * [CAUTION] means one or more unfriendly targets are suspicious of your presence and are searching for you. After a time the enemy will dismiss the disruption and the state will return to [HIDDEN] . Pickpocketing is disabled for the enemy searching for the player. Attacking in this state will not cause a sneak-critical hit.
 * [DANGER] means your presence is made known to hostile NPCs, but they do not know your current location. They will actively seek you at or around your last known location. If [DANGER] is flashing, it means that the enemy can currently see you and will engage you. The state can be returned to [HIDDEN] by moving away and staying out of sight for a long period of time. Note: As soon as the conditions are satisfied for any state it replaces the one above it on the HUD even though the player may still be in the [HIDDEN] state to several targets around them. Essentially, it reports the worst detection state towards the Player of all potential targets. Once all targets that satisfy the most-elevated state are killed (as in you kill everyone actively pursuing you in [DANGER] ), the state will revert to the highest remaining state amongst the remaining targets.

Factors in successful sneaking

 * Sneak skill: The sneak skill applies whenever the player crouches. The higher the player's Sneak skill, the easier it is to remain undetected while attacking, stealing, or picking someone’s pocket.
 * Cloaking fields: The Stealth Boy and Chinese stealth armor will wrap the user in a cloaking field that makes him or her more difficult to detect while sneaking, rendering the player virtually undetectable by visual sighting. The stealth field effect is extremely powerful, and its value matters very little, so the Chinese stealth armor's stealth field of 5 works almost (but not quite) as well as the Stealth Boy's 75. It should be noted that this field only increases one's sneaking ability, and the field will be negated if the player breaks sneak mode in any conventional manner, such as firing a loud gun, since the cloaking field does not mask sound-based detection. The stealth suit only has a +15 sneak versus the Stealth Boy's +100, but its effects are not limited by time. Cloaking can also be stacked, so the stealth armor and Stealth Boy can give a player a combined field of 80.
 * Enemy's Perception: Enemies with low Perception are easier to sneak around than enemies with high Perception. A target's Perception will be impaired (a -4 reduction) if they have a crippled head.
 * Line of sight: While out of sight an enemy can only detect the player through sound.
 * Light level: The player is more difficult to see in dark areas or at night if outdoors. If the Pip-Boy light is active, it will make the player much more visible.
 * Distance: The farther away the player is from the target(s) the less likely he would be detected.
 * Movement: The player is hardest to detect when motionless and easiest to detect when running. You are able to avoid the sound aspect of this by getting the perk Silent Running. Moving faster while within line of sight will still make you easier to spot, but you will no longer get any penalty for movement speed to your sound made. NOTE: Moving the camera (and thus moving your body) counts as movement, but not as much as movement over ground. If you are in shadows with a direct line of sight to a target not aware of your location, moving the camera may very well cause the target to investigate, or immediately spot you.
 * Contact: Touching or running into targets while crouched will immediately alert them to your location. Regardless of how hidden you are, if you bump into a target, friendly or otherwise, you will immediately be detected. This also applies to robots that have been deactivated using the Robotics Expert perk.
 * Equipped weight: The total weight of all equipped items (weapons count only if they are in your hands) makes your footstep noise louder for non-player characters. Silent Running removes this penalty entirely, allowing you full sneaking ability in any equipment. You will still hear your footsteps while sneaking with the perk, but non-player characters never will.
 * Sound: Most guns make noise. Louder guns make you easier to detect. The silenced 10mm pistol, BB gun, dart gun, Infiltrator, Perforator, all melee weapons and all unarmed weapons are considered entirely silent, and thus will not break sneak mode. Grenades will also not break sneak mode, as they do not make a noise at your location. Hitting but not killing an enemy with silent weapons still causes a CAUTION alert. All other weapons will most likely be heard, depending on your distance from the target. Missile launchers and Fat Man units make noise at your location and then at the impact point as well. Oddly enough, your Pip-Boy's radio has no effect on sneaking.

Pickpocketing
While sneaking and "hidden", pressing the "activate" button while facing a non-player character (when in touching range) will allow you to pickpocket them; in other words, steal items that they are personally "holding." This will open the inventories of both you and your target. Items can be transferred either way, and thus items can also be planted on non-player characters (also known as reverse-pickpocketing).

For each item the player character steals or plants in a non-player character's inventory, there is a chance of being detected (presumably based on the player character's sneak skill, Luck, item weight/value and the non-player character's Perception). If detected, the non-player character will automatically reclaim the item(s) taken and the player character will not be able to pickpocket that non-player character again (at least not straight away - leaving the area and returning 24 hours later should allow the player character to re-attempt this).

The player character cannot steal items a non-player character currently has equipped. To steal an item the non-player character is wearing or using (armor or weapon), the player character can reverse-pickpocket a better item (higher DR for armor, higher damage value for weapons) into their inventory and then leave and re-enter the area. The non-player character will equip the item with the highest stats and then the player character may try to steal the item he or she was using before. For melee weapons, reverse-pickpocket a better ranged weapon onto the non-player character along with the appropriate ammunition. When the non-player character is reloaded, it will equip that weapon and unequip the melee weapon. Steal the melee weapon and the ammunition you gave them, and reload the non-player character. The non-player character will be unarmed and the player character can steal the ranged weapon back. Keep in mind that just because the player character can do more damage with a specific ranged weapon doesn't mean that the non-player character will (usually but not always). Experiment to get the desired effect.

Successfully stealing the ammunition from an non-player character with a gun equipped will immediately render that non-player character unable to fire their gun. The amount of ammunition an non-player character is carrying will not match the amount they could fire if not pickpocketed (which is actually unlimited as long as they have 1 round for that weapon); this discrepancy can be attributed to gameplay purposes. This tactic can be used to influence the outcome of both non-player character/PC and non-player character/Non-player character conflicts. Concerning non-player character/Non-player character conflicts, this allows you to remain non-hostile to non-player characters on both sides of a conflict (by not needing to intervene with gunfire) while still ensuring victory for one side or another. Mind that after some time, possibly the general respawn period of 72h game time, ammunition will be restored on NPCs.

Non-player characters will notice you pickpocketing other non-player characters, hence the DETECTED sneak state, but in large open areas one can maneuver into gaps or around corners to avoid line-of-sight and return to HIDDEN. Non-player characters lying in beds may appear to have their back to you and still detect you, this is because as far as the game is concerned they are not facing the way they are lying down, that is merely an animation. To get "behind" an non-player character lying in bed, go to the foot of the bed.

The player can also use pickpocketing offensively to plant a live explosive. This will detonate after a short time, automatically killing the target regardless of the player's explosive skill or the target's health or resistances.

The Mothership Zeta add-on added another way to pickpocket a friendly non-player character. Reverse-pickpocket a cryo mine or cryo grenade onto the non-player character. After exiting the pickpocket menu, the cryo charge will go off but only stun or knockdown the non-player character. The non-player character can then be pickpocketed like any disabled target, with the exception that the non-player character won't turn hostile when he or she recovers.

Stealing Items
Picking up non-player character owned items (ie. items whose text name is red) in the game world while sneaking and [HIDDEN] will allow you to steal items undetected, though karma penalties may still apply.

Ways to increase Sneak

 * Permanent
 * Leveling up (up to 10 + INT + 3 with Educated perk))
 * Bobblehead - Sneak (+10)
 * Chinese Army: Special Ops Training Manual (+1 or +2 with Comprehension)
 * Thief perk (+5 with each rank)
 * Tag! perk (+15)
 * Silent Running perk (+10, removes movement speed penalties to sneak)
 * Survival Expert perk (+0 - +6, depending on quest results)
 * Temporary
 * Fire ant nectar (+2-8 depending on current Agility, a perfect Agility of 10 will see no benefit.)
 * Recon armor (+5)
 * Shady hat (+5)
 * Poplar's hood (+10, additional +2 if less than 10 Agility)
 * Stealth Boy (+100, +75 cloaking field)
 * Chinese stealth armor (+15, also adds +5 cloaking field while crouched)
 * Lag-Bolt's shades (+3)

Sneak in quests and exploration

 * 25 Sneak can be used to convince Trudy to fight the Powder Gangers as an alternative to 25 Speech.
 * 50 Sneak is required to smuggle improved holdout weapons into New Vegas Casinos as well as the interrogation room at Camp McCarran.
 * 50 Sneak is required to convince Mr. Holdout to sell you improved holdout weapons.
 * 75 Sneak is needed to convince Father Elijah that hiding in the Sierra Madre is easy, and effectively get him to come down into the Sierra Madre Vault.

Ways to increase Sneak

 * Permanent
 * Leveling up (up to 10 + INT/2 + 2 with Educated perk)
 * Chinese Army: Special Ops Training Manual (+3 or +4 with Comprehension perk)
 * Agility Implant (+1 depending on current Agility, a perfect Agility of 10 will see no benefit)
 * Tag! (+15)
 * Skilled (+5)
 * Temporary
 * Fire ant nectar (+2-8 depending on current Agility, a perfect Agility of 10 will see no benefit.)
 * Recon armor (+5)
 * Stealth Boy (+100, +75 cloaking field)
 * Chinese stealth armor (+5)
 * ¡La Fantoma! (+10 or +20 with Comprehension perk)
 * Assassin suit (+10)
 * Salt-Upon-Wounds' helmet (+5)
 * Stealth suit Mk II (+15 or +25 with the Firmware 1.1 Upgrade)
 * Dead Horses stalker armor (+5)
 * Blood-Nap (+10)

Lionheart
Sneak determines your character's ability to sneak around without being detected.

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