From Halopedia, the Halo wiki
The Z-2500 Automated Protection Drone (Z-2500 APD), or Autosentry, is an automated Forerunner combat support drone.
The Z-2500 is a stationary automated drone that is materialized through hard light. It can provide combat support and protection in combat. It currently outstrips similar devices used by the UNSC by virtue of its mobility and power. It is commonly utilized by Promethean Knights but can be obtained and used by Spartans to provide suppressive fire and open new tactical opportunities.
The drone is composed of an anti-gravity drive located at the lower back which provides pivoting hover movement in a stationary position, a firing lens located at the very front, and a pair of targeting arrays located at the lower front. In War Games, the targeting arrays and firing lens take the color of the team the controller is on. In the field, however, they are light blue. When it detects a target, it emits a noise and a red light.
The Z-2500 APD can be fooled by a hologram, and will fire on the hologram. The Z-2500 APD can also be avoided by a completely stationary target using active camouflage. A camouflaged target will be detected and targeted if they are moving however, and activating camouflage when already targeted will not cause the autosentry to lose its lock.
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