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{{Weapon Infobox
| image=FileCombine Sentry Gun.jpg|130px
| image2=
| name=Combine Sentry Gun
| affiliation=Combine
| manufacturer=
| model=
| type=Autonomous sentry weapon
| damage=3 (per bullet)
| magazine=
| magtype=
| maxammo=Infinite
| fire=
| ammotype=
| operation=
| rate of fire=High
| recoil=
| spread=
| projectile speed=Fast
| accuracy=Medium
| range=
| maker=
| usedby=*Overwatch Soldiers
*Alyx Vance
*Gordon Freeman
*Rebels
| counterpart=Other CategorySentry weapons|sentry weapons
| counterwep=*Gravity Gun
*Grenades
*RPG
| entity=npc_turret_floor
| designer=
| hidep=
| hidet=
| hideu=
| hideg=
}}
{{Quote|I can reprogram these turrets to attack the enemy. You set them up to defend the control room.|Alyx Vance|Half-Life 2}}
'''Combine Sentry Guns''',''Half-Life 2 Prima Guide'' referred to by Overwatch as '''sterilizers''' and as '''turrets''' by Rebels, are fully autonomous tripodal pulse weapons used by the Combine to guard choke points and vital areas.
==Overview==
FileDepot Sentry firing.jpg|left|200px|thumb|A Combine Sentry Gun firing at Overwatch forces in the Depot.
Turrets are one of many human technologies adapted by the Combine for their own use after the Seven Hour War. The guns are often deployed as static defenses, used to guard areas that are infrequently patrolled, or as a means to supplement a larger defense network. The guns are fitted with small handles and are light enough to pick up and place by hand. When not in use, they are generally stored in small forcefield-equipped lockers.
Combine Sentry Guns, however, have a number of key differences from the HECU Sentry Gun|model used by the HECU in ''Half-Life''. Mainly, their targeting systems are more sophisticated. The Combine Sentry Gun does not rely on laser tripwires, instead incorporating a visual sensor into its main body, with which it can immediately detect intruders in its sight line. Once activated, it will sound an alarm and, after a brief delay, will open fire. Upon losing sight of its target, the gun will scan the area ahead by moving its upper body back and forth, before returning to its inactive state if the target does not reappear after several seconds. This variety of gun also incorporates a limited A.I. which is somehow able to distinguish between Combine forces, humans and Xen aliens. Another key difference is that the Combine Sentry Gun has a narrower field of view and range of motion, whereas the HECU Sentry Gun is able to rotate and fire in nearly any direction.
An individual gun's programming can be accessed and modified remotely through a separate computer terminal when necessary. In ''Chapter 9a, Entanglement'', Alyx Vance reprograms a number of Sentry Guns, allowing Gordon Freeman to set them up to protect himself against protracted Overwatch assaults.
The Sentry Gun is loaded with the Combine's ubiquitous pulse ammunition, of which it has an essentially limitless supply, although in Episode One, some Combine Ceiling Turret|ceiling-mounted variants with no ammunition remaining are encountered in a zombieCity 17 Underground|infested underground. Sentry Guns cannot be destroyed, and must instead be knocked over, whether by explosives, gunfire, the Gravity Gun, or by getting close to them and knocking them over manually. Once knocked over, the Sentry Gun's targeting systems will malfunction and the turret will shoot wildly and sound its alarm for a few seconds before shutting down, much like the Aperture Science Sentry Turret.
Its unstable tripod base defect was only noticed after manufacturing.
On the body the alphanumerics "V952" can be seen, also featured on other Combine devices.
They feature a small colored light near the barrel that shows their current status
*Red - Enemy spotted (Open fire)
*Orange - Scanning area
*Green - "Sleeping" state (No threat detected)
==Appearances==
===''Half-Life 2''===
Sentry guns are first seen in the chapter ''Nova Prospekt (Chapter)|Nova Prospekt'', where the Combine make frequent use of them to slow Gordon's progress and impede the Antlion Soldier|Antlions he takes with him.
In the chapter ''Entanglement'', Alyx reprograms sentry guns to attack Nova Prospekt Prison Guard|prison guards, there are three locations where the player needs to use the sentry guns to defend themselves.
Sentry Guns were also deployed extensively in City 17 after The Uprising.
===''Half-Life 2 Episode One''===
During ''Episode One'', Sentry Guns are seen in the Hospital, protected by a Force Field and Hopper Mines, with a metal cabinet holding them in place, making them considerably more dangerous.
===''Half-Life 2 Episode Two''===
In ''Episode Two'', two Resistance members, Griggs and Sheckley, reprogram two sentries to ignore them and attack antlions. Bored during their time at the underground outpost, and with nothing else to do, they decorated the Sentry Guns with graffiti and Wikipedianose art|nose art. These guns later prove invaluable in fending off an extended Antlion attack; however, being damaged and crudely repaired with duct tape and baling wire, they short out and explode in the middle of the attack.
Another one can be seen in The Junk Yard, protected by some barrels and crates near a house.
Another three sentry guns can be seen in the White Forest base, deployed by Combine soldiers.
==Tactics==
Sentry guns can be taken down by many weapons, however the ease of this, and the weapon best suited to knocking them over, varies depending on the situation. When stood behind them, it is recommendable to use either the Crowbar or Gravity Gun to knock them over, as this uses no ammunition. When at distances, and when they are stood in front of walls, it is easiest to throw MK3A2 Grenade|grenades at them, which can often take out more than one at once.
Sentry Guns are powerful enemies but are limited by the simple fact that they can only fire at targets in their sight line and cannot move. When encountered, it is important to consider tactics; the Sentry Gun is immobile, and from behind can be taken down more easily.
In Nova Prospekt, Gordon has control over Antlions, which can be used as cannon fodder against the Sentry Guns and to distract them while the player runs or sneaks around. If there are enough Antlions, and one or more survives the Sentry Gun's constant shooting, they will attack the Sentry Gun like they would any other enemy and knock it over, thus shutting it down.
After Alyx reprograms the turrets in Nova Prospekt it's possible to carry a turret around and use it as a shooting weapon with unlimited ammo. Doing so limits Gordon's ability to do other actions such as open doors, however, so the turret needs to be put down frequently.
During ''Entanglement'', it is also possible to carry the sentry guns forwards to the Teleportation Chamber. As a result, by the end when trying to defend the teleportation chamber, Alyx and Freeman can have up to eight Sentry guns to defend their positions. One should be careful while doing this, however, since the activated sentry turrets you bring in will shoot at and kill Eli Vance|Eli and Judith Mossman|Mossman.
==Trivia==
* Reprogrammed Sentry Guns only recognize Gordon Freeman|Gordon and Alyx Vance|Alyx as friendly, and will kill other friendly NPCs.
* If a deactivated Sentry Gun is placed upright, it will re-activate.
* A glitch occurs when disabling the AI in-game, where doing so disables the sentry's AI permanently. Sentries will not react, even if "AI_Disable" is entered again to resume AI.
*Except for the fact that they can be reactivated by standing them upright, Sentry Guns are functionally identical to the Aperture Science Sentry Turret. However, Sentry Guns lack the friendly voice of the Aperture Science model, and use pulse ammunition instead of conventional bullets. However, if the Combine turrets are spawned in Portal, their firing sounds and effects will be those of bullets, just like the Aperture Science turrets.
* The beta design with temporary textures (see gallery below) for the Sentry Gun was re-used in the Source game "Alien Swarm" as an actual weapon called the IAF Sentry Gun.
* All Sentry Guns spawned via console will be hostile towards the player, as Reprogrammed Sentry Guns cannot be spawned by console since all Reprogrammed Sentry Guns are scripted.
* Friendly Sentries behave slightly different when knocked over; They do not fire any shots, and will emit a low tone and a flashing red light. This can help players find their Sentry and recover it.
==Gallery==
===Pre-release===
FileCombine sentry gun beta.jpg|Beta Sentry Gun, with temporary textures.
FileCombine sentry gun beta2.jpg|Beta Sentry Gun, closer to the final model.
===Retail===
FileGround turret rebel 1.jpg|Reprogrammed Sentry Gun seen in Victory Mine.
FileGround turret rebel 2.jpg|Ditto.
FileD3 c17 070001.JPG|Sentry Guns targeting Zombies in a City 17 building.
FileEp1 c17 02a0087.JPG|Sentry Guns protected by bars in the Hospital.
FileTurret antlions mine.jpg|Reprogrammed Sentry Guns firing at Antlions in the Victory Mine.
===Other===
FileHl2 beat turretstandoff2.png|"Warden Freeman" icon.
FileCity 17 logo retail.svg|City 17 logo featured on its bodywork.
==List of appearances==
*''Half-Life 2'' {{1st}}
*''Half-Life 2 Raising the Bar''
*''Half-Life 2 Episode One''
*''Half-Life 2 Episode Two''
==References==
{{Reflist}}
{{Weapons}}
{{Combine}}
CategoryHalf-Life 2CategoryCombine weaponsCategoryWeaponsCategoryHalf-Life 2 Episode OneCategoryHalf-Life 2 Episode TwoCategorySentry weaponsCategoryPulse weapons
