Sentry Gun

The Sentry Gun is an unmanned weapon capable of autonomously acquiring and defeating 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 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 disables 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 bombsite. 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.

Pros and Cons between the Predator Missile and Sentry Gun

 * Both require 5 kills (4 with Hardline)
 * A Predator Missile is controlled by a laptop, leaving the player on the ground and easily killed, whereas a Sentry Gun can be placed to kill an opponent. Nevertheless, both can leave the player defenseless while using. However one will be more vulnerable while placing a Sentry since they will stand out very clearly for as long as it isn't placed, a Predator Missile will only leaves the player vulnerable when controlling it, which could be anywhere between 2-5 seconds.
 * If the player dies while placing a sentry turret, it gets placed where they died. When the player dies while controlling a Missile, it will still be controlled.
 * Predator is a better way to get the immediate kills needed, but a well placed Sentry Gun can get far more kills than the missile. Predators can only get as many kills as there are players on the other team, and it is very, very unlikely that all opposing team members will be killed in one Predator.
 * Predator Missiles can destroy almost any killstreak, including a Chopper Gunner, or even with extreme luck an AC-130. A Sentry Gun can destroy some killstreaks like Attack Helicopters, but require some assistance and altitude.
 * A Sentry Gun can't detect a Cold-Blooded player. A Cold-Blooded player is still visible by the user controlling a Predator Missile, but the red box indicating a hostile is removed.
 * A Sentry Gun automatically disables itself after 90 seconds even if untouched, no matter how many players it has killed. A Predator Missile can be saved for later, but the killstreak button or switch weapon button needs to be pressed just before the Missile Camera is entered.
 * A Predator Missile's kills add to the players killstreak count. Only the first sentry gun called in will add to their killstreak.
 * The player has only one chance to use the Predator Missile, if they fails, they lose an opportunity to gain a couple more kills for a higher killstreak. The Sentry Gun can be placed anywhere valid; set it up and it does its job, making it easier to leave alone and still get many kills.
 * Due to the fact the Sentry Gun glows yellow when being placed, players setting up the Sentry Gun can be spotted quite easily and, if attacked or stabbed from behind, the Sentry Gun can be quickly disabled.
 * If the player dies while the Sentry Gun glows red when re-locating it, the Sentry Gun will disappear.
 * The Sentry Gun can only be received via an airdrop, which leaves open a very real danger of the player being killed and the package being hijacked by an enemy. Even if a team mate "saves" the package. there is no guarantee they will place it in a suitable place, and furthermore any kills they achieve with it will not count for the player who actually called it in. The Predator missile, on the other hand, does not require an airdrop, and therefore has no such complications.

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.

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 can disable 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, which allows for a overall easier mission.
 * The Sentry Gun has a 180 degree angle within which it can engage targets.
 * There is a limit of 32 total Sentry Guns on a map.
 * 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 # 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 to find out that it will be completely unharmed.
 * Sentry Guns are not known to exist in modern times, as said in the MW2 Artbook, given when the player buys the Hardened or Prestige edition of Modern Warfare 2.
 * The Sentry Gun is the only killstreak operating on the ground. All others are Air Support.
 * There is a glitch where kills from a Care Package Sentry Gun will count towards a player's killstreak.
 * The Sentry Gun in the mission "Exodus" can be picked up.
 * In Black Ops the Sentry Gun was said to have inspired the Death Machine, a portable version of it, and also a weapon in Sharpshooter.
 * in black ops you can see that it has a thermal camera on top to detect enemy players