Sentry Bot (Fallout: New Vegas)

Sentry bots are robots found in the Mojave Wasteland and Big MT.

Background
Sentry bots (military serial numbers SB-XXXX) are military robots made before the Great War with the express purpose of participating in the heaviest of firefights. Where the Mister Gutsy is a hovering platform with modest armour plating and the Protectron a push over, the sentry bot is a powerhouse, equipped with stordy armour plating, powerful weapons integrated into its chassis and benefits from high mobilty thanks to wheels mounted on its three legs.

Its successor (manufactured only in limited amounts) is the bipedal Mark II sentry bot.

Technology
Similar to their Fallout 3 counterparts, they have two arms that end with deadly weapons (a minigun or Gatling laser on the right arm, and a missile launcher on the left arm), and tripod legs with wheels. Like their Fallout 3 counterparts, sentry bots have armored heads and receive less damage from headshots. They are programmed with an authoritative, professional military personality, in contrast to the "gung-ho" personality of the Mister Gutsy model.

Sentry bot
Sentry bots are armed with arm-mounted miniguns or Gatling lasers and missile launchers, have thick armor plating, and are very fast. Although not as common as they were in Fallout 3, they can still be found in various parts of the Mojave Wasteland that contain robotic guardians such as the sacrificial chamber in Vault 11 (depending on your level) or in the Securitron vault.

Hardened sentry bot
A Hardened sentry bot is a hardened version of the military sentry bot. They are encountered along with hardened Mister Gutsies around the Crashed Vertibird in the Mojave Wasteland. Hardened sentry bots have nearly twice as much health as a standard sentry bot (500 hit points as opposed to 300 hit points). However (possibly due to a developer oversight) despite what the name might suggest, they are completely unarmored with a DT of 0, unlike a standard sentry bot which has an innate DT of 18, and thus can actually survive less damage than a standard model sentry bot. One result of their increased raw health is a greater resistance to pulse grenades.

Prototype sentry bot
An antique, prototype version 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.

Excerpt from the description of the antique model in REPCONN HQ's museum:

"Whoa, watch your step! You don't want to be facing this fearsome fellow if you accidentally stumble into a restricted area. Whether sporting the latest in dual miniguns, rockets, or laser cannons, the Sentrybot not only takes its job seriously, it also takes no prisoners! It's proof of RobCo's commitment to defense that these deadly guards are concealed in chambers throughout this facility, so let this be a warning: Watch where you step, or out'll come RobCo, guns blazing!

Exhibit Brought to You By Your Friends at RobCo"

RY-589 ultimo bot
A unique sentry bot that appears in the Fallout: New Vegas add-on, Old World Blues, and is much stronger than other variants. It is found patrolling outside of the X-7a "Left Field" Artillery Launch.