Sentry Gun

The Sentry Gun is a Killstreak reward featured in Call of Duty: Modern Warfare 2 and Call of Duty: Black Ops.

Overview
The Sentry Gun is an unmanned weapon capable of autonomously acquiring and firing upon enemy targets by using thermal detection. It, as well as the UAV and Predator, is indicative of the increasing role of unmanned technology on the battlefield.

Campaign
M5 Sentry Guns are seen in Call of Duty: Modern Warfare 2's campaign various times. They first appear in the level "Wolverines!". The Sentry in this level is positioned on top of Nate's Restaurant, where it provides autonomous cover for Sergeant Foley and his team during the recovery of codename "Raptor". Ramirez (the player character) can reposition the sentry gun if needed. An enemy sentry gun is seen in "Exodus", so this may be a clue that the Ultranationalists made an exact copy of the Sentry Gun, since the Sentry gun is likely to be a unique weapon, made only for US Military. Parts of a sentry gun can be found throughout Makarov's safe house in the level "Loose Ends". Sentry guns can also be found during the level "Endgame" on one of the banks during the boat chase before the player goes through the cave.

Special Ops
Sentry guns are only available for use in the levels "Homeland Security", "Wardriving" and "Wreckage". They are used in Homeland Security to defend from inside of the gas station and adjacent building. They are used in Wardriving to guard the locations of the computers as the files are downloaded. They are used in Wreckage to kill enemies and destroy the vehicles.

Multiplayer
The Sentry Gun is a multiplayer killstreak reward in Call of Duty: Modern Warfare 2. After achieving a killstreak of 5 (or 4 with the Hardline perk), a player may call in a helicopter that will airdrop a package (similar to the Care Package killstreak) containing the Sentry Gun. After acquiring the package, the player can place the gun in the location of his/her choice. It can detect enemies at a moderate distance, with its cone of fire centered on where its user positions it. The turret can be picked up and moved; the turret is disabled while held, and the player is unable to use weapons or other equipment. If not destroyed, the turret will expire after 90 seconds, appearing to short-circuit itself.

Any players with the Cold-Blooded perk will not be targeted by the turret (though they are still vulnerable to shots fired at other targets). The sentry gun can be disabled with a single melee hit or by gunfire. A flashbang or stun grenade will disable the Sentry Gun for a few seconds, leaving it vulnerable to knife. It can also be avoided by moving around its flank, outside of its firing arc. A riot shield user can approach the sentry gun and knock it down with the shield bump, or let the gun destroy itself with ricochet hits. A certain number of destroyed sentry guns will remain on the map and will only vanish when more sentry guns are placed. These destroyed guns form a visual distraction, both because players will approach them cautiously as it's hard to tell if a gun is active or disabled and because they are so bulky, allowing players to hide behind them. They can, however, be fired and walked through. The EMP disables the sentry gun permanently.

In objective-based games such as Capture the Flag or Sabotage, the Sentry Gun can provide valuable support while protecting a flag or bomb-site. Even on Hardcore, the gun can absorb a decent amount of gunfire before being destroyed. However, it can be destroyed by indirect fire through Predator missiles or other aerial support weapons. Despite the nature of Hardcore giving players much less health, the Sentry Gun is not very effective on hardcore because most players are using cold-blooded, or can easily avoid the Sentry Gun, then either disable it, or just keep away from it.

Sentry Guns can be beneficial for snipers for numerous reasons. First, Snipers can only have one claymore (Without Scavenger or One Man Army) to cover them while they snipe. Sentry Guns can provide cover for the sniper rather than a claymore meaning the player does not have to sacrifice a Frag grenade, Throwing Knife, etc. for a claymore. Also, unlike claymores where the enemy can come in quite close, sentry guns can keep enemies pinned down at a distance and thus, not allowing the enemy to get in close enough to shoot the player at an angle or throw a grenade at the player. Sentry guns can be moved by the player at any time before they are disabled, even if the player has been killed since placing the gun.

Sentry guns have 1000 health points and no damage multipliers. Melees destroy them instantly, explosives do 7x their base damage to them. (so if an AT4 does 160 base damage, it will do 1120 damage with a direct hit to a sentry gun). Bullet damage is the same as normal

Call of Duty: Black Ops
The Sentry Gun is a killstreak in Call of Duty: Black Ops. It requires 6 Kills, unlike 5 in Call of Duty: Modern Warfare 2. It still is required to airdrop it in. The Sentry Gun crate can no longer be changed using the Hardline Pro ability due to a patch (PC and Wii can still change it using Hardline Pro). Enemy players using Hacker Pro can turn your Sentry Guns against you if they can get close enough. Players using Ghost Pro will not be targeted by the Sentry Gun, although if the Ghost user stands between the Sentry and an ally, they will be shot by the resulting crossfire.

The Sentry Gun is an unpopular killstreak for many players, due to the relatively high killstreak required, the ease at which enemies can kill/capture/disable it, and the fact it must be airdropped in. For these reasons, many players pass over it in favor of other killstreaks. This can be frustrating for players who are looking to unlock Ghost Pro, as one of the challenges involves destroying an enemy Sentry Gun. Because so few players use Sentry Guns, this challenge can take a long time to complete. To counter this, players have often used sentry guns as one of their own killsteaks and given it to the enemy for their use. By doing this, the likelihood of obtaining Ghost pro increases because it increases the frequency of Sentry guns in play for a player to destroy, so long the player can earn them.

Zombies
The Sentry Gun (a.k.a. Automatic turret) is one of the three traps available on Kino der Toten. There are 2 in the level. One is in the Theater by the Teleporter which can be activated for 1500 and stays on for approximately 2 minutes. The other one is in the Foyer room, on a table in the lower area. It can be activated for 1500 points and will stay activated for approximately 90 seconds. It will engage any zombie around it, pivoting 360 degrees. If it targets a zombie and the player is obstructing line of sight, it can hit the player and deal damage. It is based on the Type 92 heavy machine gun from Call of Duty: World at War. It can also be found in Dead Ops Arcade as a power-up. There are a few automatic turrets scattered across Ascension.

Trivia

 * Two sentry guns with no tripod can be found on the mission "Loose Ends" inside the weapons cache room, although it is not usable. It clips through the ammo box and the shelf partially.
 * The original sentry gun concept art used a XM312 machine gun instead of a M134 minigun.
 * An EMP disables Sentry Guns.
 * A Sentry Gun can acquire and destroy helicopters and Harriers. It can even acquire an AC130, but cannot destroy it.
 * The Sentry Gun has a Picatinny rail attached to it. However, no upgrades are actually available for the gun.
 * In the single player level "Wolverines!", the Sentry Gun can be moved.
 * The Sentry Gun has a 180 degree angle within which it can engage targets. The exception to this is in the Zombie map Kino der Toten, where it turns 360 degrees.
 * There is a limit of 32 total Sentry Guns on a map at a time
 * If a player is playing Spec Ops and is killed while holding the sentry gun they will still be carrying it while they are down. Enemies will shoot at it providing great cannon fodder for the other player.
 * Upon reading the writing on the ammo box of a Sentry Gun, one will notice that the writing says "600 Cartridges// 7.62 IW Sentry // Infinity = M1920", followed by a serial number.
 * To earn this killstreak's challenges (the ones earned by "calling in" a number of them), the player must use the actual killstreak. The player cannot earn them by obtaining the Sentry Gun through a Care Package or Emergency Airdrop.
 * The barrels do not spin in multiplayer, even when firing.
 * If holding a sentry gun when an EMP goes off, it can be put down and it will be completely unharmed.
 * In Modern Warfare 2, the Sentry Gun is the only killstreak operating on the ground. All others are Air Support.
 * There was a glitch where kills from a Care Package Sentry Gun would count towards a player's killstreak.
 * The Sentry Gun in the campaign mission "Exodus" can be picked up. This can be done by throwing a flashbang near it, and rush towards it with a high-mobility weapon and pick it up. If the player wants to accomplish this, it's advised to do it on Recruit, as many Russians protecting it will attack the player, so he would die on higher difficulties. NOTE: it never fires against Ultranationalists, instead it fires towards the US forces.
 * In Black Ops the Sentry Gun was said to have inspired the Death Machine, a portable version of it.
 * In Black Ops the Sentry Gun has a small camera on top that resembles the Camera Spike's camera.
 * It also has a radio similar to the Radar Jammer.
 * In Black Ops a sentry can be destroyed by a Ballistic Knife, along with the tomahawk.
 * In zombies the Sentry Gun was inspired by the Call of Duty: World at War mods/custom maps for PC.