Aperture Laboratories turret.
The turrets (to distinct from the rocket turrets named sentry turrets or sentry guns) are tripodal guns that are generally used as sentries. They are employed by Aperture Science and have little AI.
Description[]
They have a thin red laser that serves as a motion sensor, though other methods of motion sensing may be used. When approached, a turret will extend its sides, revealing some of the innards and four small short-range firearms. There are two on each side though it seems only 1 of the two can fire at a time. Turrets also have a large capacity for ammo, but may be restocked from time to time. When a target is lost or eliminated, the sides retract once more.
Turrets have several prerecorded phrases that are played at certain events. For example, when a target is spotted, you may hear something like "I see you," or "Target acquired."
Generally turrets are very easy to disable, requiring only to be tipped out of an upright position. (though, this does not apply to caged turrets). They have an automatic gyroscope that cannot be reset after it has been changed too drastically, so generally turrets must be dispensible. When tipped, a turret will play a phrase (usually something like "malfunctioning" or "hey") and rapidly fire until it is fully disabled.
P:AAA turrets[]
Turrets in P:AAA are essentially an upgrade. The turrets can be reset if stood upright, and a further 3rd version can have no beam coming out from it's eye, making them more similar to the Combine turrets in functioning.