Turret

Turrets are Security Devices that function as Rapture's automated defense systems. They're stationary contraptions designed to shoot intruders on sight which can also be hacked by the player, turning them over to their side.
A hacked Turret will not target Big Daddies or Security Bots unless they are hostile to the player. If an unhacked Turret is in the area, the two devices will shoot each other until one of them is destroyed.