Constructor Sentinel
From Halopedia, the Halo wiki
Constructors are devices similar to Sentinels in purpose, and Plasma Pistols in appearance, that mainly repair damage to any Forerunner structure they find, using weak energy beams similar to Sentinel Beams.
The Sentinels will come to their aid if they are attacked, as they are ill-suited for combat. However, their beams will damage someone if they get caught in the path (on legendary their beams can kill in seconds but still not enough for complete and devastating death). They also can use their beams to lower the shields on pistons, allowing them to move throughout the Sentinel Wall quickly. Constructors are encountered only during the level Sacred Icon, but they can be seen on The Oracle.
