Pepper gun

The Pepper Gun is a riot control weapon used by security forces. It can stun a target for a few seconds without causing long-term damage. It does not affect MJ-12 Commandos nor monsters.

The Pepper Gun is first found near the front of the Statue of Liberty on the first mission. If not obtained there, it can be found in the MJ-12 base in Hong Kong.

Ironically, UNATCO, a so-called peace-keeping organization, almost never issues Pepper Guns.

Tactics
In a pacifist run, Pepper Spray is useful if you need to get a backshot on a target, but have already alerted him. It's also useful if you're running low on mini-crossbow and/or riot prod ammo and need to run away.

In a non-pacifist run, it can be used if you need a fast (organic) target to stop moving long enough to kill them more easily, a good way to conserve ammo. It's also useful against multiple enemies in close quarters; spray two or three guards to incapacitate them, then deliver a head shot to each without taking fire.

It can also be used on certain laser-beam tripwires to bypass them without triggering them: the spray can block the beam without triggering the security device, allowing you to crouch, spray, and slide past undetected. Unfortunately, only a minority of triggers are susceptible to this trick and there's no way to tell without risking setting the trap off.

In-game Description
The pepper gun will accept a number of commercially available riot control agents in cartridge form and disperse them as a fine aerosol mist that can cause blindness or blistering at short-range.

Pistolet pieprzowy