Unidentified ancilla (Installation 05)
From Halopedia, the Halo wiki
This unidentified ancilla is a Forerunner construct that monitored a Flood containment facility on Installation 05. It was far larger than a monitor; rather than freely levitating like a monitor, this construct was mounted on rails on the ceiling of the facility.
This ancilla might have served as a local caretaker designated to watch or oversee the Flood specimens contained in the facility.
Given their remarkably similar appearances, it is also possible that this ancilla had the same role with the Knowing, a Forerunner construct on the planet Ariel that was designed to gather and organize information about the course of history. If this is so, it is possible that all Halo installations possess such a construct.
The ancilla is attached to a pair of rails on the ceiling of the main room in the multiplayer map Cold Storage. It serves as an invulnerable piece of immobile scenery. It follows the movements of any players in the room, but stops paying attention to players when they leave the room. However, it will not track players in edit mode unless it sees them prior to entering this mode. It is capable of seeing players using active camouflage, implying the usage of heat sensors or other optical technologies. It will continue to track the bodies of dead players provided if no one else is in the room.
List of appearances