Sentry bots (military serial numbers SB-XXXX) are security robots made before the Great War with the express purpose of participating in the heaviest of firefights during war. Where the Mister Gutsy is a hovering platform with modest armor plating, and the protectron was originally designed for protecting business premises, the sentry bot is a powerhouse, equipped with sturdy armor plating, powerful weapons integrated into its chassis and high mobility, thanks to mecanum wheels mounted on its three legs.
Sentry bots are one of the highest level robot characters, and are much more powerful opponents than protectrons, robobrains and Mister Gutsy models. Their purpose is mainly to guard locations for high profile characters and organizations, such as REPCONN in Fallout: New Vegas. In Fallout 3 they will be more encountered in office buildings and pose a serious threat, wielding missile launchers and Gatling lasers. Three standard variants exist. The Fallout 2 variant is shaped like a bipedal mech, standing about the height of a super mutant and is capable of walking. The Fallout 4 variant is much bulkier, can accommodate dual mortars, and has a cooldown mode that is activated if the robot fights for too long.
Slightly darker in appearance when compared to the normal variant, the Enclave model boasts improved systems. They appear at Raven Rock and alongside Enclave squads in the wasteland. During Broken Steel they are encountered guarding Adams Air Force Base.
Military robots from before the Great War, painted in the characteristic olive green of the U.S. Army. They can be encountered at Fort Constantine, the National Guard depot and when wandering around the wasteland.
This unique sentry bot is encountered in Broken Steel, at the end of the Presidential metro, near the metro to Adams Air Force Base. It holds the main fuse, which is needed to repair the nearby powerbox for the metro.
An antique prototype version that can be found in the museum inside REPCONN headquarters. It has four wheels instead of the standard three, a set of arms stemming from its back and arching around over its shoulders. Where the arms would normally join the main body in current models, it includes 3 jets on each side, as used by Mister Gutsy/Handy robots.
It is similar to the military sentry bot in appearance, but is differently colored, with orange eyes instead of the standard red. The NCR sentry bot was originally intended to be stationed in Camp McCarran, evident in its G.E.C.K. id McCarranFieldSentryBot, but was cut from the final version of Fallout: New Vegas.