Forerunner automated turret
From Halopedia, the Halo wiki
File:1771119-Medium.jpg
A turret killing a grunt
The automated turret is a form of equipment so far only encountered on The Covenant (Level) and Halo (Halo 3 Level) in the game Halo 3. It resembles a stripped-down sentinel, and fires a thin, blue, sentinel-beam-like beam at enemies. However, due to programming issues, it has major problems picking out targets and more often follows allies with its targeting system, and does not fire.
