Sneak (Fallout)

	For a cross-game overview of this skill, see Sneak.

Sneak is a skill in Fallout, Fallout 2 and Fallout Tactics. It determines the chance of being detected while sneaking.

Initial level[]

Fallout[]

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

Fallout 2 and Fallout Tactics[]

${\displaystyle \text{Initial level}\%=5+\text{Agility}\times3}$

Description[]

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 without the Silent Running perk.

How close one can sneak to a target before detected depends on a combination of several factors:

Fallout and Fallout 2[]

• Target's Perception statistic.
• Sneaking character's Sneak skill.
• The facing of the target.

Target facing has a direct impact on how close a player character can be before the target begins to check if they can see a sneaking player (Sneak Checks). The player can sneak up to 60% closer to the target from behind before facing Sneak Checks against the target's perception and sneak skill. While it is not entirely clear what factors affect making a sneak check, the rest of the sneak formula is known:^[1][2]

${\displaystyle \begin{align} Location &= \begin{cases} 5, & \text{if sneaker is in front of watcher and not using a Stealth Boy} \\ 2.5, & \text{if sneaker is in front of watcher and using a Stealth Boy} \\ 2, & \text{if sneaker is not in front of watcher and watcher is in combat} \\ 1, & \text{if sneaker is not in front of watcher and watcher is not in combat} \\ \end{cases}\\ SneakinessM &= \begin{cases} \frac{1}{4}, & \text{if successfully sneaking} \\ \frac{2}{3}, & \text{if unsuccessfully sneaking} \\ 1, & \text{if not trying to sneak} \\ \end{cases}\\ SneakinessA &= \begin{cases} 1, & \text{if successfully sneaking and }Sneak > 120 \\ 0, & \text{if not successfully sneaking or }Sneak \le 120 \\ \end{cases}\\ PerceptionRange &= Location \times Perception \times SneakinessM - SneakinessA \end{align}}$

Successfully sneaking or not involves a sneak skill check; it's not known exactly how this skill check is performed, but ignoring modifiers that would add or subtract percentage points, the baseline is the player's skill expressed as a percentage, up to a maximum of 95%; on a success, the player will have to roll again in 1 in-game minute, while on a failure, the player will have to roll again in an amount of time based on their skill (more skill means the player can try to be successfully sneaking sooner):

• Success: 60 seconds
• Failure:
  • Skill<= 80: 60 seconds
  • 81<=Skill<=100: 40 seconds
  • 101<=Skill<=135: 30 seconds
  • 136<=Skill<=170: 20 seconds
  • 171<=Skill<=200: 15 seconds
  • 201<=Skill<=250: 12 seconds
  • 251<=Skill: 10 seconds

Calculating aggregate odds of failing to sneak repeatedly and incorporating that into the skill delay gives the following formulae for how long it will take the player to begin successfully sneaking and accordingly what percentage of the time they spend successfully sneaking:

${\displaystyle \begin{align} AverageDelay &= \left(\frac{100}{min\left(skill,95\right)}-1\right)\times delay \\ TimeSneaking &= \frac{60}{AverageDelay + 60} \\ &= \frac{60}{\left(\frac{100}{min\left(skill,95\right)}-1\right)\times delay + 60} \end{align}}$

Or:

• 80: 80%
• 81: 86.48%
• 95: 96.61%
• 101: 97.44%
• 136: 98.27%
• 171: 98.70%
• 201: 98.96%
• 251: 99.13%

Fallout Tactics[]

• Target's Perception statistic.
• Sneaking character's Sneak skill.
• Sneaking character's stance plays a much smaller role than the above two factors,
• The light level from the day/night cycle plays a small factor too, but again a much smaller one than the Perception statistic and the Sneak skill.
• Contrary to Fallout and Fallout 2 the facing of the target does not matter at all.

References[]

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