A widespread and popular model in RobCo Industries' line of products, the Protectron was designed as an inexpensive work drone, capable of performing a wide variety of tasks such as construction, firefighting, and office duties. Some models were designed for security and have defensive capabilities.
A bipedal, ambulatory robot capable of instigating combat, the Protectron has a transparent faceplate with several blinking red lights within. Breaking its faceplate reduces its accuracy. If the Protectron is inactive and a melee weapon is used, the chance of breaking this barrier increases.  The dome that serves as their head scans surroundings, and two arms appendages serve as both laser and melee weapons. The upper-body of a Protectron can swivel to either side, and can change direction of movement by way of two legs.
All Protectrons are constructed with a combat inhibitor mounted on their back that allows them to selectively target opponents. The combat inhibitor can be disabled. When the combat inhibitor is crippled, the robot will frenzy, automatically engaging any nearby targets. Protectrons take reduced damage from shots directed at their head, but damage to the rest of their chassis is taken normally. When a Protectron has lost a limb arm or leg, its audio system will also sound damaged as the robot will speak but with some audio garbled.
If both of the Protectron's arms are destroyed, it will initiate a self-destruct sequence. The unit will begin to glow yellow and explode shortly thereafter. Legendary Protectrons also self destruct in this way.
Each Protectron has a programmable personality, each serving a different role. This can be set to default, fire brigadier, law enforcement, medical responder, construction worker or subway steward.[clarification needed] Personalities can be changed remotely without having to shut down the Protectron.[clarification needed]
The personality changes the behavior of the Protectron, what it says as it patrols, and creatures it attacks:
Default: Will be any of the five other personalities that are initialized on them.
Fire Brigadier: Attacks anyone carrying weapons (and certain junk items that are fire hazards) in their inventory.
Law Enforcement: Attacks anyone who un-holsters their weapon and fires a shot.
Construction Worker: Attacks characters not wearing a work helmet (or any helmet such as the army helmet).
Medical Responder: Attacks any hostile creature and anyone who attacks it first. Will not heal anyone but would "resuscitate" them with electrical melee attacks.
Subway stewards: Attacks hostiles and the player character if they do not give it a subway token immediately upon request, or do so by way of reverse-pickpocketing.
The standard Protectron can use its arm lasers to attack foes from a distance, or swat foes away for a substantial amount of damage when up close. If their arms are destroyed, they will initiate their self-destruct sequence and waddle toward their enemies in a last-ditch attempt to take them out. Appears in green, blue and tan.
This Protectron model is equipped with an internal "cryo-gun" which it can utilize in battle. Before the war, it was utilized to suppress fires. Attacking anything near the robot will cause it to become hostile. If the Sole Survivor is equipped with a Molotov cocktail, the Protectron fire brigadier or any Protectron set to fire brigadier personality mode will warn that the item they are holding is possibly a fire hazard and should be disposed of. Found at outside the Boston Police rationing site, Robotics Pioneer Park and inside D.B. Technical High School.
This type can be distinguished by its yellow hazard color scheme with a light on their heads. In close range combat, it will attack its target with simple punches. If its target is outside of melee range, it will attack with one or two nail guns (similar to the railway rifle), rapidly firing spikes. It can also be spawned with two cargo loading arms that deal a large amount of melee damage. If the Sole Survivor is wearing a hard hat or mining helmet, the Protectron will note how they are wearing proper safety equipment for the location they are in.
Police Protectrons are similar to the utility variants due to the fact that they have reinforced plating over their inner workings. They can be distinguished due to their blue paint job. These Protectrons utilize a stun gun or electric shock in close range combat.
Doom Protectrons are even tougher variant of the Protectron devil, with proportionally stronger melee attack and laser damage. As with the other variants, they are usually seen with Rust Devils or other Rust Devil Protectrons.
Protectron basilisks are very high level encounters, with heavily armored chests and legs. They wield a railway rifle in their right arm and a flamer in their short left arm. The right wrist, arm and leg plates are spiked and serrated, causing their melee attacks on targets to leave them bleeding. Their heads are tall, like a spiked crown, with the skull of a human on the lower part. They can be seen accompanying legendary Rust Devils, assaultron gorgons or Mister Handy war machines.
Unique to Nuka-World amusement park, five variants include Nukatrons, Nukatron watchers, guardians, defenders, and sentinels. They resemble Nuka-Cola machines with a monitor at the top, sometimes playing a "Park Safety Rules" promotional video complete with audio.
Galactrons are another variant of the Protectron added in Nuka-World in the Galactic Zone. Although marketed as "never-before-seen prototypes", Galactrons are, in reality, customized security Protectrons with a custom white and gold paint job and enhanced laser weapons.
Protectron control terminals can be loaded with the Protectron override program holotape which gives additional options when linked with active Protectrons. There are three options: "Disengage Safety Sensors," "Override Alliance Parameters" and "Hijack VIP Escort Protocols." The first option reverts the Protectron to view all entities as hostile, including the Sole Survivor. The second option sets the Protectron to be friendly towards the Sole Survivor and any companion(s), and hostile to their enemies. The third option, which appears when the holotape is loaded into a terminal, sets the Protectron to be a temporary follower. This option will not be present when loaded into the Pip-Boy, only when loaded on the terminal connected to the charging station.
When hacked to follow the Sole Survivor, if the player character moves quickly, Protectrons will waddle towards them faster than normal to catch up.
Hacked Protectrons do not regenerate health over time.
It is possible to encounter a radioactive Protectron. The Sole Survivor will take radiation damage from being in close proximity to this Protectron whether it is hostile to the Survivor or not. This radioactivity can sometimes interfere with their ability to hack the Protectron's controlling terminal if the terminal and Protectron are in close proximity.
In Robotics Pioneer Park, there are two shacks, one with a leveled deathclaw and one with the four models of Protectron in it, and an Advanced terminal. If the latter is set to defend, they can engage the deathclaw in combat.
If the Sole Survivor is wearing a hard hat or mining helmet while a utility Protectron is active, the Protectron will note how they are wearing proper safety equipment for the location they are in.