A sentry gun is an autonomous device capable of tracking and engaging targets with an integrated weapons system. While often depicted with firearms, some less-than-lethal systems exist, such as motion-sensing deterrents for wildlife that use a water hose or paintballs. At the other extreme, systems for protecting naval vessels may wield chainguns and guided missiles.
More sophisticated systems can distinguish between valid and invalid targets (such as vehicles or small animals). Systems designed for military use would likely benefit some means of distinguishing between friendly forces. Otherwise, advance warning would be needed to avoid the system's area of protection.
— In-game description
All enemy infantry, light vehicles, or sentry guns within its 90° sight cone will be targeted. However, it can barely tilt its gun in the vertical axis, and can only focus on one target at the time. The A12 Enforcer will fire at visible targets out to medium ranges, but is most effective against targets within 50 meters. Past this, it will do lower damage and have significant spread. This makes the sentry well suited for area denial in narrow areas, like alleyways or corridors. It can be particularly effective at defending the reactor corridors on-board Titans, due to their cramped and narrow nature.
The chief counters to the A12 Enforcer are explosives and EMP attacks. V5 EMP Grenades will deactivate the sentry for several seconds, long enough for it to be destroyed by gunfire. FRG-1 Grenades are also particularly effective, as players can toss them at the sentry while in cover and can quickly overwhelm the sentry. Both the Mitchell AV-18 and Sudnik VP can destroy it with one hit. The A12 Enforcer also takes a while to deploy (2-3 seconds), which makes it difficult to deploy while under fire. As a result, the sentry should be placed before engaging and in a location that is hard to notice in order to ambush players. In other locations, the Support player who placed it must be in a position to cover it so he can take out targets who are actively trying to destroy the sentry.
- Main article: Boris
- When aboard a Titan, sentry guns may detect nearby enemies through walls and proceed to target them; its tracers will go through the walls but it will do no damage. This can potentially be used as a pseudo-motion sensor to locate enemies, however hostiles will also be aware of the sentry's position as a result.