Created by RobCo, protectron robots were designed (as their name suggests) for protection, although they can also be seen being used in a manual labor role as well. Typically used in office-type settings, their secondary programming is modular, making them useful as greeters, ticket collectors, bartenders, celebrity or historical figure impersonators, even sexual partners. Typically used in office settings, a large variety of available synthetic personalities and programming options made them universally useful. RobCo offered personalities like the R04 V9 "office helper" with the ability to process and track office protocols and agendas in real time, RobCo RS3 V4.1.6 "utility helper" with automatic routine download and pest extermination mode, RobCo RX2 V1.16.4 "vault helper", loaded with Vault protocols. Other models of public service protectrons include medics which are outfitted with a defibrillator, firemen using an internal cryo gun, police officers with electric shock and melee capabilities, and even heavy-duty construction workers utilizing internal nail guns. In terms of combat, protectrons are usually weak and easy to defeat, because of their weak weapons and slow movement speed.
In Fallout 4, protectrons are usually found in charging pods attached to terminals that must sometimes be hacked to activate them. The terminal software allows for different "personalities" to be uploaded to the unit, which changes the unit's voice dialogue and weapons loadout. The choices are: Default, Subway Steward, Construction Worker, Medical Responder, Firefighter, and Law Enforcement.
Some attributes of the protectron's looks were derived from 1950's comic books, which keeps with Fallout's overall retrofuturistic theme.
Unlike protectrons in previous games, the Commonwealth variant (except the police, medic, construction, and fire brigadier models) appears to have a transparent "faceplate" made of plastic or glass, with several blinking red lights visible behind the faceplate. It is possible to break this plate by fully damaging the head, which in turn 'blinds' the protectron, reducing its accuracy. If the protectron is inactive and a melee weapon is used, it will increase the chance of breaking the faceplate. Previous versions had an opaque metal faceplate with a lit up glass dome on top.
Protectrons have a glass dome on top of their heads that acts as an ocular lens which allows the protectron to scan its surroundings and act accordingly. In each "hand" is a laser emitter that shoots a high-powered laser. The upper-body of a protectron can swivel up to roughly 90 degrees to either side before having to step into a different position.
All protectrons come with a combat inhibitor mounted on their back that allows them to selectively target opponents. The combat inhibitor is generally left exposed, making it easy to disable when approaching a protectron from behind. When the combat inhibitor is crippled, the robot will fly into a frenzy, automatically engaging the nearest possible target, regardless of any previous affiliation.
Compared to previous games, protectrons have become significantly sturdier, particularly so against ballistic damage. However, by attacking their limbs, their more vulnerable insides will be revealed, which can be attacked for extra damage. 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 with the force of a mini nuke or a car shortly thereafter.
Protectrons take reduced damage from shots directed at their head. Damage to the rest of their chassis is taken normally.
Legendary protectrons, like other legendary robots, will detonate violently, similar to a mini nuke blast, approximately two seconds after they are destroyed.
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.
This model possesses two static electricity generators on its hands which are intended to be used as defibrillators. Protectron medics lack any ranged armament, but are deceptively powerful at melee range. They can attack targets with a staggering flurry of electrified slaps followed by a two-handed power attack.
This protectron model is equipped with an internal "cryo-gun" which it can utilize in battle. Before the war, it was intended to stop fires. If any firearms are fired near it, then it will attack. If the player character 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 fire hazardous and should be disposed.
A somewhat stronger and more powerful variant of the original protectron, this type can utilize dual laser arms in combat and a better melee attack. This protectron is not to be messed with at a low level. It can also appear in several different colors.
They may have one or two nail guns, similar to the railway rifle. They have an orange hazard color scheme with a light on their heads. They also have reinforced plating on their heads and backs originally designed to protect them from construction hazards but now protect them from whatever they may fight in the wastes. In close range combat, it will attack its target with simple punches. If its target is outside of melee range, it will instead utilize its nail guns, rapidly firing spikes that can kill even a high level player character with a single shot. It can also be spawned with two cargo loading arms that deal massive melee damage.
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 of some description in close range combat.
Similar to the protectron and protectron watcher, this variant is the toughest type of any protectron. It can use both dual rapid lasers, punches, and strong bashes. For low level players the best course of action is to avoid it
Protectron scourges are a tougher variant of the protectron devil. With a stronger melee attack and better laser damage, these types could be quite difficult to defeat at a low level. They are usually seen with Rust Devils or other protectron scourges.
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. The left arm and leg plates are reinforced to prevent much ballistic damage. Their heads are tall, like a spiked crown, with the skull of a human baby on the lower part. Their waist has a standard plate. They can be seen accompanying legendary rust devils, assaultron gorgons or Mister Handy war machines. If prepared, they can take down a behemoth or an integrated tankbot.
Protectron golems are an even stronger variant of other rogue protectrons. With an even stronger melee attack and even better laser damage, this protectron variant shouldn't be messed with at low levels. Again, seen with Rust Devils and other protectron golems.
A type of protectron unique to Nuka-World. This protectron type shoots weaponized Nuka Cherry/Cola Quantum blasts instead of lasers. It's head and torso are combined into one, with a small screen on the upper torso presumably serving as its primary interface. The screen will sometimes play the "Park Safety Rules" promotional Nuka-World trailer, complete with audio. When this portion is scavenged and put on a robot workbench it removes the option of adding a separate head. Their voices are different than that of a regular protectron, and are much softer and slower.
Identical in appearance to other Nukatrons, this variant has much higher stats and patrols the Galactic Zone of Nuka-World. With three-and-a-half times the amount of health as the normal Nukatron, this variant can prove to be deadly.
Identical in appearance to other Nukatrons, this variant has the highest stats and patrols the Galactic Zone of Nuka-World. The Nukatron sentinel has four times more health than the normal Nukatron and shoots deadly bursts of weaponized Nuka-Cherry and Nuka-Quantum.
Unnamed protectron sheriffs do not appear anywhere in Nuka-World, but they can still be spawned with the console. However, named protectrons Sheriff Eagle and Sheriff Hawk do appear in Dry Rock Gulch, manning the entrances as tour guides.
In Fallout 4, each protectron has a programmable personality so that it can serve a variety of roles: default, subway steward, law enforcement, fire brigadier, medical responder, and construction worker.
Generally, the personality does change the behavior of the protectron, and what it says as it patrols (construction workers will make comments about workplace safety and attack characters not wearing a work helmet, and medical responders will make comments about injuries and be generally passive until attacked). Medical responders will not heal player injuries and all variants will attack hostile NPCs on sight.
The only notable change is that subway stewards will insist on seeing the player character's subway token and will attack when if is not produced (regardless of whether one is present in their inventory or not). To give the subway token to the subway protectron, one must press the action button/key immediately following the bot's request. There is a window of approximately .8 seconds to give the coin (Video Demonstration).
Personalities can be changed remotely without having to shut down the protectron.
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, protectrons will comically waddle towards the player unfeasibly quickly if the player moves too far away.
Hacked protectrons do not regain health over time.
It is possible to encounter a radioactive protectron. Whatever the logic behind this radioactivity is (faulty power supply?), 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 the Survivor's 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 are set to defend, they will quickly and easily kill the deathclaw.