Sentry gun The sentry gun is a gun that is automatically aimed and fired at targets that are detected by sensors . Fictional sentry guns have appeared in science fiction since the 1940s . Video games have provided a fertile ground for fictional visions of sentry guns . Fictional examples of automatic sentry guns have appeared since the 1980s , in films such as " Aliens " ( 1986 ) and the television series " Æon Flux " ( early 1990s ) . The earliest functioning military sentry gun was the Phalanx CIWS , a radar - guided gatling gun platform that defended ships from missiles . In fiction . Literature . A sentry gun is used to pin down a group of rebelling colonists in Robert A . Heinlein ' s 1949 novel " Red Planet " . Michael Crichton ' s version , in the 1969 novel " The Andromeda Strain " , fired tranquillizer darts at intruders in the underground facility . Later , in 1995 , Crichton wrote about a more advanced vision of sentry guns in his book " Congo " . Video games . Video games have provided a fertile ground for visions of sentry guns . Although sentry guns first appeared in the " Command & Conquer " series , the " Team Fortress " mod for " QuakeWorld " solidified the sentry gun ' s position in gamers ' vocabularies . Another early game that featured the sentry gun was " Goldeneye 64 " . Various games — such as " Duke Nukem " , " Metal Gear " , and " " — have several versions . In the Team Fortress series of games the engineer class can construct and later upgrade sentry guns . The latest incarnation of the TF sentry gun starts as a high - caliber cannon , upgradeable with machine guns and rocket launchers . The spy class has a tool ( the Electro - Sapper ) specifically designed to neutralize sentry guns and other buildings . Games like Timesplitters and F . E . A . R . feature sentry guns that appear as obstacles to the player , and also feature instances where the player can remotely commandeer these sentry guns to turn against enemies . Sentry guns also play a big role in the series of " Alien vs . Predator " video game . In the alien - part of the game , you run many times in the line of the gunsight , and you have to find a solution to shut them down or destroy them . In the game " Battlefield 2142 " , the support class can unlock a sentry gun as one of its 3rd level unlocks . Squad leaders are able to employ sentry drones ( also a 3rd level unlock ) , whose targets are designated by squad members through NetBat . In both " Half - Life " and " Half - Life 2 " , many levels involve destruction or even control of sentry guns . " Portal " , also made by the creators of the Half - Life game series prominently features sentry guns that deliver humorous dialogue in high - pitched electronic voices . The game BioShock features sentry guns in machine gun , rocket launcher , and flamethrower varieties as well as security bots summoned by security cameras which are essentially sentry guns with rotors allowing them to fly like small helicopters . All sentry devices in the game are able to be hacked or bribed by the player to serve himself . The game Perfect Dark features enemy sentry guns that must be destroyed in order to advance in the game , in addition to a player - usable version disguised as a laptop computer . In the space - based MMORPG Eve Online , the areas surrounding stations and jump gates are lightly defended by sentry guns similar to CIWS systems . The relative security ( although inefficient against a coordinated attack ) enjoyed by players in the so - called " Low security space " zones , as opposed to " 0 . 0 space " where PvP can freely occur , is largely due to the presence of these sentry guns . In the space - based PC game Freelancer jump gates , trade lane rings and space stations are equipped with low - power sentry guns , however , they are called turrets and thus may be human - operated . Descent Freespace and Freespace 2 are also noted for having sentry guns . The Terran , Vasudan , and Shivan races all have their own sentry guns , with the GTSG Mjolnir class being specifically designed to take down enemy warships with a large beam weapon . In Crysis ' multiplayer Power Struggle mode there are sentry guns equipped with machine guns and missile launchers to prohibit the player from entering the enemy base . In the game Call of Duty Modern Warfare 2 , a Sentry Gun is awarded to a player who achieves a five killstreak in a life without dying . In Homeworld and Homeworld 2 3D RTS game , many captital spaceship protect itself using CWIS ( point defense system ) . in addition , sentry probes can be placed around the map which will become immobile , and shoots anything near it . Sentry Guns are also a reward given to players in the multi - player mode of Call of Duty : Modern Warfare 2 , if having picked the correct option the player can place one of these on the map after having killed 5 other players in a row . This fictional weapon is designated the M117 Sentry . Film and television . Fictional examples of automatic sentry guns also appeared in the Special Edition version of " Aliens " . In the film , marines who were surrounded by hostile alien creatures barricaded themselves into a sick bay facility , and deployed sentry guns to block access points to the sick bay . The weapons successfully repelled the alien adversaries until they ran out of ammunition . All references to this sequence were deleted from the theatrical print of the film , though Alan Dean Foster ' s 1986 novelisation of the movie contained this scene . The sentry gun sequence was reinstated for the extended Special Edition cut of the film , released initially on VHS in 1988 and much later on DVD . As mentioned above , the film adaptation of " Congo " depicted a fictional laser - sighted remote sentry unit , which was used to repel the enemies . The science fiction television series " Æon Flux " depicted accurate sentry guns in multiple episodes . In the show , these guns , along with concrete walls , are depicted as a series of Fortifications separating two nations . Military use . Phalanx close - in weapons systems . The earliest functioning sentry gun was the Phalanx close - in weapons system ( CIWS ) , a radar - guided gatling gun platform that defends ships from missiles . There is a land - based version of the Phalanx CIWS , also used for missile defense . Similar to the Phalanx is the Goalkeeper CIWS , a more powerful version with the same purpose . According to the United States Navy , Phalanx is the only deployed close - in weapon system capable of autonomously performing its own search , detect , evaluation , track , engage and kill assessment functions These guns perform sentry duty against missiles , but are not in line with the fictional versions of the sentry gun that are used primarily against humans in books , movies , and video games .