Perception

 is one of the seven Primary Statistics in the SPECIAL system.

Fallout, Fallout 2, Fallout Tactics
Modifies: Sequence, ranged combat distance modifiers and the First Aid, Doctor, Lockpick, Traps and Pilot skills. A player character with higher Perception may notice things that allow them to open up new dialogue options on occasion. It also determines how far away your character starts from hostile critters in random encounters.

Perception is required for many perks, notably PE 8 for Sniper in Fallout, Fallout 2, Fallout Tactics.

In Fallout 2, Perception can be raised with the Green memory module using ACE (+1, permanent) and Mentats (+2, temporary).

Fallout 3

 * Modifies Explosives, Lockpick and Energy Weapons skills

Perception determines how far away you can detect enemies on your compass (enemies show as red bars). When playing with a high Perception, you will be able to "sense" your enemies even before they come into view.

Having enough perception can yield dialog options with some NPCs, such as Moira Brown, Mel and Machete.

Perception-Based Perks
The benefit of the Survival Expert perk is affected by what you say to Moira Brown after each portion of The Wasteland Survival Guide quest. Having a perception of 7 yields relevant "smart" dialog options at the end of the Contract Radiation Sickness and Traversing a Mine Field objectives.

Ways to increase Perception

 * The Perception Bobblehead can be found in the Museum of Dave at the Republic of Dave, located in the extreme northeastern area of the Wasteland.
 * The perk Ant Sight can be obtained from completing the quest Those!, which permanently increases perception by 1.
 * The Intense Training perk will allow you to increase your Perception (or any other S.P.E.C.I.A.L. stat) once for each time that you take it by one point.
 * The Night Person Perk increases your Perception and Intelligence when the sun is down
 * Wearing certain pieces of armor such as Maple's Garb, Vance's Longcoat Outfit, and various pieces of headwear will increase your Perception by 1.
 * Mentats and Orange Mentats can be used to temporarily increase Perception by 5.

Fallout: New Vegas
Perception affects the distance at which your character is able to detect other creatures. It also factors into a few Speech checks.

Ways to increase

 * Coyote Tobacco Chew
 * Mentats
 * Party Time Mentats
 * Hat-like Headgear (eg. Pre-war Ball Cap)
 * Implants (New Vegas Medical Clinic)
 * Intense Training Perk
 * Night Person Perk
 * Glasses (with Four Eyes trait)
 * Stealth suit Mk II