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"I can reprogram these turrets to attack the enemy. You set them up to defend the control room."
Alyx Vance[src]

Combine Sentry Guns,[1] referred to by Overwatch as sterilizers and turrets by the Rebels, are fully autonomous tripodal pulse weapons used by the Combine to guard choke points and vital areas.


Depot Sentry firing

A Combine Sentry Gun firing at Overwatch forces in the Depot.

Turrets are one of the 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 force field-equipped lockers.

Combine Sentry Guns, however, have a number of key differences from the original model in Half-Life. Mainly, their targeting systems are more sophisticated. The Combine Sentry Gun does not rely on laser tripwires. Instead, they incorporate visual sensors into their main bodies which immediately detects intruders in its line of sight. 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 turrets also incorporate a limited A.I. which is somehow able to distinguish between Combine forces, humans, and Xen creatures. 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 themselves against protracted Overwatch assaults.

The Sentry Gun is loaded with the Combine's ubiquitous pulse ammunition, of which it has an essentially limitless supply. However, in Episode One, some ceiling-mounted variants have run out of ammunition in a zombie-infested underground. Sentry Guns cannot be destroyed and must instead be knocked over, whether through use of 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.[1]

On the body the alphanumeric "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)


Half-Life 2

Sentry guns are first seen in the chapter Nova Prospekt, where the Combine make frequent use of them to slow Gordon's progress and impede the Antlions he takes with him.

In the chapter Entanglement, Alyx reprograms sentry guns to attack 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 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 malfunction and explode in the middle of the attacks.

Another one can be seen in The Junk Yard, protected by some barrels and crates near a house.

Additionally, three sentry guns can be seen in the White Forest base, deployed by Combine soldiers.


  • Sentry guns can be taken down by many weapons, depending on the difficulty and the weapon best suited to knocking them over. When standing behind them, it is recommended to use either the Crowbar, the Gravity Gun, simply bumping into it or picking it up and then throwing them knock them over as these methods use no ammunition. When at far distances and when they are front of walls, it is highly recommended to throw grenades at them, which can often take out more than one instantly.
  • 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 plan carefully. The Sentry Gun is immobile and can be taken down more easily from behind.
  • In Nova Prospekt, Gordon has control over the 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 can survive the Sentry Gun's constant shooting and they will attack the Sentry Gun and knock it over, thus shutting it down.

As a Defense Weapon

When reprogrammed to become friendly, the Sentry Gun is useful for defense purposes against most enemies. Regardless, a friendly turret has the same weaknesses like enemy turrets.

  • After Alyx reprograms the Turrets in Nova Prospekt, players should put the Turrets in specific spots where they can perform well, best at long ranges as they will mostly kill enemies before they can rush up close and knock the turrets down. If not possible, try to put these Turrets in the corner of the walls so it will be harder for the soldiers to disable them.
  • Storage lockers can be used, turn the gun around to face you and put it in the locker. therefore it cannot be knocked over.
  • Most of the time, available storage units only contain a few Sentry Guns and there may be some areas in which it cannot be guarded with a sentry gun. Because of this, the player needs to defend some unguarded areas by themselves. If the area is not guarded, enemies may rush from that area and flank the turrets and/or attack the player.
  • Be warned when a Combine soldier approaches the Sentry head-on, he will most likely throw a hand grenade at medium ranges, so be ready to press the "USE" key or, better yet, use the Gravity Gun to launch the grenade back at the soldier. If a Soldier is armed with a shotgun and approaches the sentry at close range, he will rush mostly recklessly, knock the turret down, and then engage the player with extremely aggressive behavior. Because of this, taking down these troops is a top priority. To make matters more difficult, soldiers can also approach a Sentry from behind and they will simply run up close and knock it down. As such, always guard areas that are not protected by sentry guns.
  • After Alyx reprograms the turrets in Nova Prospekt, it's possible to carry a turret around and use it as a weapon with unlimited ammo. Doing so limits Gordon's ability to do other actions such as opening doors thus the turret needs to be put down frequently.
  • During Entanglement, it is also possible to carry the sentry guns towards 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 since the activated sentry turrets the player brings in will shoot at and kill Eli and Mossman. However, this does not happen in the XBOX version and it has since been patched on the PC version.
  • In Episode Two, the player needs to defend Griggs and Sheckley's outpost. Always bring a turret to an area where the Antlions will attack from. If there are more than two points where Antlions comes from, put a turret in an area where it is not guarded. One turret is sufficient enough to take a group of Antlions down.

Behind the scenes

  • The reason reprogrammed Sentry Guns only recognize Gordon and Alyx as friendly is because in the level editor multiple entities are created called "ai_relationship" and in the settings of these entities it refers to the Subject(s) as "npc_turret_floor" and the Target(s) as "!player" for the player and "npc_alyx" for Alyx Vance.
    Ai relationship

    Icon used in the Level Editor.

    After that, there is a disposition setting (Which has 4 options, Like, Hate, Fear and Neutral). This is set to "Like" so that all Floor turrets will not attack the player or Alyx. After this is done another "ai_relationship" is created with the same Subject(s) and instead of the player and Alyx set in the Target(s) "npc_combine_s" is set with a Disposition of "Hate". The same method is done for "npc_combine_s" to "Hate" the Floor turrets. That way the two are in a state of opposition.
  • The reason in the PC version (pre-patch) the turrets attacked Eli and Mossman was due to no "ai_relationship" targeting "npc_eli" or "npc_mossman" with a disposition of "Like" in the level. Still, today, if a player carries a turret from the first defense segment to the last, that turret will attack Mossman and Eli. Eli can be killed with this method, blocking progress in the level.

Related achievements

Hl2 beat turretstandoff2 Warden Freeman (10G)
Survive the second turret standoff in Nova Prospekt.


  • If a deactivated Sentry Gun is placed upright, it will re-activate.
  • Friendly Sentries behave slightly different when knocked over; they do not fire and will emit a low tone and a flashing red light. This can help players find their Sentry and recover it.
  • In Half-Life 2 for the Xbox, Xbox 360 and PS3 it is currently impossible to " destroy " the sentry. In Half-Life 2: Episode 2 and Garry's Mod it is possible for the turret to be destroyed as when destroyed it will start to beep red then explode into little pieces. In Half-Life 2 however the turrets cannot be destroyed but instead turned over or onto the side.


List of appearances


  1. 1.0 1.1 Half-Life 2 Prima Guide
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