Sentry Gun

{{Weapon Infobox
| image=FileSentry on.jpg|220px
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| name=Sentry Gun
| affiliation=*Hazardous Environment Combat Unit
*Black Ops
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| type=Autonomous sentry gun platform
| damage=
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| maxammo=Infinite
| fire=
| ammotype=
| operation=
| rate of fire=High
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| spread=
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| entity=monster_sentry
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| hidep=
| hidet=Yes
| hideu=Yes
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The '''Sentry Gun''' (also known as '''Tripod-Mounted Chaingun'''''Half-Life Prima Guide'') is a fully autonomous tripodal weapon featured in ''Half-Life'' and its expansions, commonly used by the Hazardous Environment Combat Unit|HECU and the Black Ops to guard WikipediaChoke point|chokepoints and vital areas. In terms of game development, it is the predecessor of the Combine Sentry Gun featured in ''Half-Life 2'' and its episodes.


*The gun consists of a powerful machine gun built onto a tripod. The gun itself rests on a turntable mechanism of sorts on the top of the tripod, which allows it to rotate 360° and fire in any direction, unlike its Combine successor, which has a narrow field of fire. Behind the gun is the ammo reserve.

*To detect its targets, the gun relies on motion detection, either through independent laser sensors that have been placed nearby (the gun is triggered when the target trips the sensor beams), or when the targets gets closer to the gun.

*Once the target has tripped the beam, the turret deploys its weapon with a high pitched whine, and fires upon any target in sight. Once activated, the sentry will remain alert for a time (it makes a steady beeping sound whilst scanning for targets) before sinking into a dormant but alert state. 

*Sentry Guns are powerful enemies, but are severely limited in mobility. When encountering one, stepping back and considering tactics is advised, as unlike other enemies, this one does not move. Looking for a way around or using explosives is a good move.

*Despite appearing gawky and unstable, these guns are in fact stronger than they appear they can take a considerable amount of damage, and are difficult to knock over. Enough of any type of damage will knock them over (a well-placed .357 Magnum shot or a Shotgun (Half-Life)|Shotgun double blast), but explosives are the most effective counter (Fragmentation Grenade (Half-Life)|Grenades, Satchel Charges, or the Rocket-Propelled Grenade Launcher (Half-Life)|RPG).

*The Crossbow (Half-Life)|Crossbow is also effective against turrets since they destroy them in one hit.

*It is also advised to avoid tripping the laser sensors as much as possible, as that bypasses fighting the guns entirely.



The Sentry Gun is introduced in the game's fifth chapter, ''"We've Got Hostiles"'', in the High Security Storage Facility in Sector D. It is featured in the eighth chapter, ''On A Rail'', along the Materials Transport in Sector E. At the end of the eleventh chapter, ''Questionable Ethics'', above the entrance to the Alien Research Labs. During the twelfth chapter, ''Surface Tension'', along the cliffs in the Black Mesa desert.

===''Half-Life Opposing Source''===

It is featured in the game's fifth chapter, ''Friendly Fire'', set up by the Black Ops to protect the Mark IV Thermonuclear Device in the Ordinance Storage Facility located above the Materials Transport.

===''Half-Life Blue Shift''===

It is first seen in the fourth chapter, ''Captive Freight'', near a M44 cargo truck, and another in the map where Rosenberg is, at the Freight Yard. It makes one final appearance in the sixth chapter, ''Power Struggle''.

===''Half-Life Decay''===

The Sentry Gun is featured in the game's fifth chapter, ''Domestic Violence'', near the bedrooms in the Level 3 Dormitories. In the bonus chapter, ''Xen Attacks'', in the Sector E Storage Facility|Ordinance Storage Facility in Sector E.

==Behind the scenes==
*Due to the physics system limitations of the GoldSrc engine, Sentry Guns simply fall over once they have taken a set amount of damage. This was improved for ''Half-Life Source''.
*The Sentry Gun's model and behavior was changed for the PlayStation 2 version. They appear to have a red flare effect on their top, just like the Automatic Turrets. They explode and leave metal pieces behind, seconds after they fall down in ''Half-Life Decay''.


FileSentry off.jpg|Inactive.
FileSentry on.jpg|In action.
FileSentry PS2 off.jpg|''PlayStation 2'' model, inactive.
FileSentry PS2 on.jpg|''PlayStation 2'' model, in action.
FileHL BMRF HighSecurityMaterialsStorage.jpg|Sentry Gun in Sector D.
FileBio lab outside.jpg|Sentry Guns outside the Alien Research Labs.
FileTruck bs.jpg|Sentry Guns near a M44 cargo truck in the Freight Yard.
FileDy dorms0046.jpg|Sentry Gun in the Level 3 Dormitories.
FileDy dorms0055.jpg|Two Sentry Gun in the Level 3 Dormitories.
FileDy alien0020.jpg|Near the Xen crystal truck in the Ordinance Storage Facility in Sector E.

==List of appearances==
*''Half-Life Day One'' {{1st}}
*''Half-Life Opposing Force''
*''Half-Life Blue Shift''
*''Half-Life Decay''

== References ==

{{Black Ops}}
CategoryHECU weapons
CategoryBlack Ops weapons
CategorySentry weapons
CategoryHalf-Life Opposing Force
CategoryHalf-Life Blue Shift
CategoryHalf-Life Decay