Sentry Mechanical Firing Device

The Sentry Gun (abbreviated to SG), officially known as the Sentry Mechanical Firing Device, and also as a Sentry or Turret, 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).

A level one Sentry Gun is a single-barrel machine gun with an internal magazine. The Sentry has a motion sensor, as stated in Meet the Engineer and the Sentry Manual.

A level two Sentry Gun appears to use an automatic cranking system to rotate the barrel, as indicated by the 2 electric cables visible. It also has 2 Gatling guns and a laser sight is built into the carbine body. Its ammunition is belt-fed.

A level three Sentry Gun is identical to the level two, with the exception of an additional set of rocket silos on the top, which comes out of the back ammunition housing area.

The Sentry Gun functions as an automated turret that fires at the closest enemy within its range and line of sight. Dealing constant as well as consistent damage with noticeable 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. If a Sentry Gun is sapped, it gains a 33% damage resistance against a Spy's weapons.