The Aperture Science Sentry Turret is a testing element in the Portal Franchise. It acts as an enemy to the player character, as it shoots the player. However, they can easily be knocked down, picked up, portalled away, destroyed by a Discouragement Beam, dropped in Goo, put in the path of a Crusher, blocked with a Hard Light Bridge, placed on an Aerial Faith Plate, fizzled in a Material Emancipation Grid, dropped from a high place, hit with an Energy Ball, put in an Excursion Funnel, put in the path of a rocket, placed in a Shredder, dropped in an Incinerator, placed near a Pneumatic Diversity Vent, dropped in Flames, placed near a Bomb, knocked over by another turret (giving the achievement Friendly Fire in certain games), carried away by an Unstationary Platform, or crushed with cubes by the player. Any of these can be useful. There are many variants, such as the Defective Turret, the Rocket Turret, and the Frankenturret. In the first two Portal games, Turrets will not shoot you if you pick them up, but in later games, this is usually not the case.
They have white outer shells, which are possibly the same material as "Portal Surfaces", and a red "eye", which emits a red laser. If the player walks into this beam, or even around it, the turret will activate, and the sides shoot outward, revealing 4 guns, 2 on each shielded "arm", and shoot. When the victim is killed, the turret will close up. However, if it leaves, the turret will search around, and attempt to find the target, then shut down. This movement is also shown if you pick up a turret, in which case it will swivel crazily and jerkily. When a turret shoots, it utilizes springs to launch the entire bullet, including casing, but a loud gunshot noise occurs anyway. A turret is balanced on 3 legs, but if it is knocked over, it proceeds to shoot in a crazy pattern, then shut down. The turret also has an antenna-like device, which serves an unknown purpose, possibly to receive orders. Defective Turrets show some interesting anatomy of turrets as well.