The Sentry Gun has a simple design, a blue-gray box placed on a small metal pipe which allows it to rotate ninety degrees and cover an entire hallway. It has an elongated barrel, with a small metal cone on the front which it uses to fire. After each burst of shots fired it'll release smoke from exhaust holes on the main cube and re-lock on on the enemy target. It never stops firing.
There's also a red version of the turret located at the Support Towers, these versions don't fire continuously at enemies.
An advanced version of the red one is located inside Haven Palace, it was equipped with a metal plate for defense making them indestructible.
Baron Praxis placed these throughout the Sewers to keep both Metal Heads as smugglers out of it. Although smaller creatures like the Znorkle Tooth and Glub still lived here they were in a relatively low ratio compared to other areas. Jak had to destroy these for Krew, so he could continue his smuggling activities. After this the amount of Metal Heads drastically increased. Now that Jak destroyed the turrets, tons of metal heads began gathering in the sewers due to there being no more danger. The sheer amount can be seen most noticeably in the mission Escort men through Sewers. After the shield walls were destroyed, metal heads rose from the sewers, and invaded the city.
The Sentry Gun has one basic attack, a burst of three shots. After this it re locks-on onto the target and fires again.
The indestructible guns constantly fire from left to right and back.
It is very easy to outmaneuver them, one can simply strafe from side to side or use long jumps to get behind their turning radius.
The third turret can only be avoided by eithe rjumping over the bullets, hiding behind a wall and waiting till it has turned away. Commonly there will be an object in the middle of it's firing radius.