Forerunner automated turret

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The Forerunner automated turret, sometimes referred to as the autoturret and auto-turret, is a Forerunner construct that was used by Builder Security similar in design to an Aggressor Sentinel. As its name implies, the autoturret acts as an automatic antipersonnel weapon. It is typically deployed by a user in a single location to act in a defensive measure. It hovers in place above the ground and will fire upon any enemy targets that come within range of its sensors. It fires blue, beam-based plasma projectiles that are naturally hot enough to melt steel.^[1] These autoturrets were encountered and used by John-117 during the Battle of Installation 00.

Gameplay

The autoturret is a very useful piece of equipment in Halo 3 for suppression. It can kill both Covenant units and Flood forms with relatively few short bursts. Its only drawback is its slow target acquisition system; the autoturret takes a few seconds to lock onto a target. Because of this, the autoturret can be easily destroyed by a squad of Covenant soldiers or a swarm of Flood forms. Its heads-up display symbol is a silhouette of the equipment itself, and slightly resembles the symbol for the power drain.
The auto-turret has enough firepower to quickly remove a Brute's power armor, kill a Jackal and a Grunt with a single shot, and kill a Brute Chieftain within three shots. The auto-turret's beam is also powerful enough to knock back any airborne enemies.
In campaign, the auto-turret's firepower increases significantly as the game's difficulty increases.
The turret has a warm-up time of about three seconds. The turret also can have difficulty selecting targets; often tracking allies with its targeting system and occasionally even shooting at the player.
When the turret is the player's enemy, the AI skill level for it is greatly increased. As with marines that become hostile to the player, it will select targets quicker, fire more accurately, and only rarely will it turn away from you on higher difficulties if you are within its sight. This can catch players offguard in the level 'Halo' as any surviving turret deployed by the player outside the control room will be hostile after defeating 343 Guilty Spark, and can kill the player within moments.
It is rather fragile, easily being destroyed by enemy forces. Additionally, it can only attack enemies almost directly in front of it.
If bumped by the player or an enemy, it may go flying upwards in an erratic manner.

Trivia

After the player defeats 343 Guilty Spark during Halo, if the player had previously deployed any auto-turrets outside the Control Room, they will turn against the player and fire at him/her.
After allying with the Flood during The Covenant, any auto-turrets the player deploys will still be hostile to the Flood.
If the player destroys a certain Fleet of Retribution Type-52 Phantom during The Covenant, any auto-turrets deployed by the player will fire at 343 Guilty Spark.
These Forerunner autoturrets are only encountered on the Halo 3 levels, The Ark, The Covenant and Halo.