The Sentry Gun, also known as the Sentry Mechanical Firing Device, Sentry, Turret, or simply abbreviated to SG, is a building that can be constructed by the Engineer using the PDA, the Engineer's build tool. The gun itself is a tripodal device constructed of metal, team-colored paint, and a laser sight (when used with the Wrangler).
The Sentry Gun functions as an automated turret which fires at the closest enemy within its range and line of sight. Dealing constant as well as consistent damage with noticable knockback and an immunity to critical hits, a Sentry Gun is the cornerstone of a successful defensive setup. On the other hand, they take a while to set up to full potential, and even a fully-stocked Sentry Gun can be destroyed with little trouble by a well-executed Übercharge or a Spy with his Sapper. Engineers must be on the lookout for such threats to ensure their Sentry Gun's survival.
The Sentry Gun costs 130 Metal to build, 200 Metal to upgrade to level two, and an additional 200 to upgrade to the third and final level totaling to 530 Metal. With each upgrade level, the Sentry Gun becomes more powerful, gaining machine guns, rockets, as well as more health. The firing range remains constant regardless of level. The Sentry Gun's ammo and health may be replenished with Metal by the Engineer hitting it with his Wrench. Each bullet reloaded costs 1 Metal and each rocket reloaded costs 2 Metal.
When placing a Sentry Gun, the limit of its range is represented by a 3D sphere of the team color with a radius of 1100 Hammer units. A Sentry Gun that is being constructed will have its health increase gradually until it reaches its maximum health upon completion. The Sentry Gun rotates 90 degrees to patrol the area, but is capable of rotating 360 degrees to lock on to a target. This takes a brief moment however, which may allow faster foes to slip past its range. The Sentry Gun can also be manually rotated to face a different direction before building commences. When the blueprint is shown, using the alternate fire button (default key: 'MOUSE2') will rotate the blueprints counter-clockwise by 90 degrees.
Sentry Guns will not fire upon enemy Spies that are cloaked or disguised. Sentry Guns will also not fire upon enemies in its range if there is a water surface between them or if the enemy is behind cover - this cover includes the Engineer's Dispenser. Sentry Guns are also unable to fire if an enemy Spy attaches an Sapper to it or while they are being upgraded/built. A destroyed Sentry Gun leaves 60 Metal worth of pieces, which can also be picked up by other classes as Ammo.
Unlike most other weapons, the Sentry Gun's weapons do not get affected with damage falloff from range, nor do they gain criticals. It is possible, however, to make the Sentry Gun deal mini-crit attacks and damage if its target is coated in Jarate, under the effects of the Fan O'War or Crit-a-Cola, or if the Engineer who built the Sentry Gun is close to a Soldier with an active Buff Banner – boosting the damage of each bullet to 22.
Included in the Engineer Update was an unlockable secondary replacement, the Wrangler, which allows the Engineer to take direct control of his Sentry Gun by "marking" targets manually. Doing so shuts down the Sentry Gun's automated target-lock system, but diverts the excess power from the targeting system into speeding up its firing rate, effectively doubling the damage-per-second of the Sentry Gun. The Wrangler also provides the Sentry Gun with a protective shield which absorbs two-thirds of enemy fire while the Wrangler is active. A wrangled Sentry Gun has no maximum range and does not suffer from damage falloff at longer ranges. Once the Engineer switches away from the Wrangler, however, his Sentry Gun is unable to fire for 3 seconds while its auto-lock targeting computer reboots. It is still shielded during this time.
Since the Engineer Update, players are able to haul their buildings around. An Engineer carrying his Sentry Gun moves 25% slower (225 Hammer units) and cannot fire or change weapons. However, a redeployed Sentry Gun retains its previous level and automatically sets up twice as fast. Engineers do not lose any Ammo or Metal by moving Sentry Guns. If the Engineer is killed while hauling his Sentry Gun, it is automatically destroyed along with him and gives a notification in the kill icon area of the screen. Sentry Guns under the effects of an Sapper cannot be picked up.
An Engineer is vulnerable to damage from his own Sentry Gun's bullets. For about the first 300 Hammer units of their flight, Sentry Gun rockets will pass through the Sentry Gun's Engineer without detonating, as if he were another member of the same team. However, if the rockets do strike another surface within this distance and explode, the Engineer is vulnerable to the resulting splash damage. Beyond this initial distance the Engineer is fully vulnerable to his own Sentry Gun's rockets. (The knockback from Sentry Gun self-damage enables the Engineer to perform bullet and Sentry rocket jumps, especially with the aid of the Wrangler.)
Combat Mini-Sentry Gun
The Combat Mini-Sentry Gun is a more combat-efficient version of the standard Sentry Gun, and is a component of the Engineer's Gunslinger unlock. It is a smaller Level 1 Sentry Gun outfitted with a rotating light and glowing checkered paint. Like the Sentry Gun, it can be hauled.
- Costs only 100 Metal to place (the normal Sentry costs 130 Metal). This allows an Engineer at a full 200 Metal to build both it and a Dispenser without needing additional Metal.
- Constructs at four times the speed of the original Sentry Gun, being armed and ready in less than 3 seconds (hitting the Sentry will NOT make it construct faster), and when deployed after hauling it will be armed in 1.5 seconds.
- Deploys at full health and continues to gain health during construction if damaged, making it more difficult to destroy before completion.
- Fires 50% faster than a Level 1 Sentry Gun.
- Can rotate 35% faster than the default Sentry Gun.
- More useful for Sentry jumping, as the firing rate and reduced damage combine to deal more knockback for an equivalent health loss.
- Has only 100 health, compared to a Level 1 Sentry Gun's 150.
- Not upgradable or repairable, though the owner and other Engineers can still refill its ammo.
- Deals only 50% the damage per shot of the original Level 1 Sentry Gun. Therefore, DPS is overall lower (48 compared to the normal Sentry Gun's 64).
- Drops considerably less Metal when destroyed.
- Once a Sentry jump is executed, not exceptionally useful as part of a base in the new area.
Sentry Gun Levels
|150 (effectively 450 with the Wrangler shielding)||130 Metal||Semi-Automatic Firing Barrel|| Damage: 16
Shots per second: 4 (8 with Wrangler)
Average DPS: 64 (128 with Wrangler)
|180 (effectively 540 with the Wrangler shielding)||330 Metal||Dual Rotational Minigun Barrels|| Damage: 16
Shots per second: 8 (16 with Wrangler)
Average DPS: 128 (256 with Wrangler)
|216 (effectively 648 with the Wrangler shielding)||530 Metal||
Dual Rotational Minigun Barrels
Target Guided Rocket Launch Support System
|100 (effectively 300 with the Wrangler shielding)||100 Metal||Semi-Automatic Firing Barrel|| Damage: 8
Shots per second: 6 (12 with Wrangler)
Average DPS: 48 (96 with Wrangler)
| Sentry Gunner|
Accumulate 10 Sentry Gun kills with a single Sentry Gun.
| Gun Down|
Destroy an active sentry gun using your pistol.
| The Argyle Sap|
Blow up an Engineer, his sentry gun, and his dispenser with a single Sticky bomb detonation.
| Midwife Crisis|
Heal an Engineer as he repairs his sentry gun while it's under enemy fire.
Destroy 3 Engineer Sentry Guns.
- The player has the ability to build the Combat Mini-Sentry Gun, while having any wrench equipped, by holding out the blueprints for the Sentry with the Gunslinger and then quickly switching to a wrench. The player will build a Mini-Sentry (it will still cost 100 Metal). This cannot be done vice versa (equipping the Gunslinger while having normal Sentry blueprints out.)
- Combat Mini-Sentry Guns share gibs with standard Level 1 Sentry Guns. This means that the light and the checkerboard pattern disappear when a Combat Mini-Sentry Gun is destroyed.
- The Combat Mini-Sentry's status in the corner of the HUD will show an upgrade progress bar despite not being repairable or upgradable.
- The 3D sphere that represents the attack range on the Combat Mini-Sentry is smaller than the normal Sentry Gun 3D sphere; however, they both have the same attack range.
- The damage of a level 3 Sentry Gun's rockets has falloff based on the distance of its Engineer to the target.
- A Wrangled Sentry does not play its rocket-reloading animation.
- Wrangling a Combat Mini-Sentry Gun might result in it remaining in the Wrangled state even when the Wrangler is not the currently active weapon. Switching back to the Wrangler corrects the problem.
- The original Sentry Gun designs were created by Radigan Conagher in 1890. The original and current designs are visually identical.
- The Engineer apparently designed and built the final version of the Sentry Gun under contract from TF Industries in 1965.
- The Sentry Gun makes a number of beeps every time it reverses its rotation. The number of beeps corresponds to its upgrade level, where a Level 3 turret makes three quick beeps. Additionally, the higher the Sentry Gun's level, the louder it is. A Level 1 Sentry Gun is slightly harder to hear than a Level 3 Sentry Gun; this fact can help attentive players find guarded areas.
- The Sentry Gun's alert noise sounds slightly different when being targeted; slight clicks can be heard along with the regular beep.
- An unused alternate kill icon for the Level 1 Sentry Gun exists in the game files, seen to the right.
- Feign deaths produced by the Dead Ringer will not be added to the Sentry Gun kill/assist counter, but will contribute to the Best Little Slaughterhouse in Texas achievement.
- Valve ordered and received a full size motion-tracking model of a Level 1 Sentry Gun from Weta Workshop.
- Loose Canon comic, page 8, Retrieved 2010-10-18