Alien

Aliens are extraterrestrial beings in the Fallout series. In 2162, the Vault Dweller can encounter a downed spacecraft and two dead aliens. In 2242, the Chosen One can encounter some things of apparent extraterrestial origin. In 2277, the Lone Wanderer can encounter aliens on the spacecraft Mothership Zeta and a dead alien at the location of the downed spacecraft, Recon Craft Theta. In 2281, the Courier can find two Aliens and an Alien Captain, the latter having and Alien Blaster (but only with wild wasteland).

Background
The Brotherhood of Steel and Shi have encountered the bodies of alien life forms or their spaceships, as did the pre-War United States government, which kept its alien specimens mostly in Area 51. By extension, the Enclave and Brotherhood Outcasts also have access to alien technology; alien power cells can be found at Fort Independence and in the armory of the Enclave's Mobile Base Crawler. They can also be found in the Citadel's armory (if you choose to destroy the Citadel during Who Dares Wins).

Finally being encountered in Mothership Zeta, they are small, greenish humanoids that are presented as malevolent creatures that seem to view humanity with contempt and will gladly vivisect their test subjects or keep them in cryogenic storage after torturing them for their scientific pursuits. The aliens themselves seem to have their own language and cannot be understood by the player in any way.

Biology

 * When engaging the aliens for the first time in your holding cell, Somah tells you to hit their heads, implying that this area is largely unprotected.
 * The aliens have no visible teeth, and live on a diet of worms and squids.
 * While their hands lack thumbs completely, the fingers are so long they can wrap around objects.
 * Aliens appear to breathe oxygen. Evidence of this is seen on Mothership Zeta as the aliens do not wear helmets when you and the other captives are breathing oxygen.

Language
The aliens speak with clicks, high-pitched squeaks and wails. The sounds sound strange and incomprehensible, but patterns may be detected in their language, and Holly Barrisford is capable of reproducing the sounds they make. Strangely, the alien distress signal sounds very different from the alien speech heard on the mothership - suggesting multiple alien languages or a code.

Combat

 * Aliens will occasionally wear helmets, even inside the ship. These do not seem to have an effect on damage resistance and appear to be merely cosmetic.
 * Inertia suppression fields are sometimes employed by aliens and significantly increase damage resistance; the amount of shots needed to kill a shielded alien tends to at least quadruple. However, the inertia suppression fields don't protect against after-effects such as Jingwei's Shocksword's shock damage or the flamer's burning damage, nor will they have any effect on a reverse-pickpocketed explosive device.
 * Aliens tend to have drones with them in some areas which heightens their threat level as the guardian drone's weapon packs a very powerful punch.

Crashed ships
Five alien ships are known to have crashed in the United States:
 * An alien ship in special encounter in California (Fallout).
 * Recon Craft Theta in Capital Wasteland (Fallout 3).
 * Another alien ship can explode over the head of the Lone Wanderer in the Capital Wasteland during the Firelance event although the cause of the catastrophe is unknown.
 * At the Citadel, there is information on a terminal (in the A-Ring) about another ship that crashed in a heavily wooded area that the government was not able to reach.(Possibly the Recon Craft Theta as the crash site is surrounded by ,dead, trees.)
 * An alien ship, with three aliens near it, just east of Brooks Tumbleweed Ranch in the Mojave Wasteland (Only with the Wild Wasteland trait) (Fallout New Vegas).

Weapons
Firearms:
 * Alien atomizer
 * Alien blaster (Two exist)
 * Alien disintegrator
 * Atomic puliverizer
 * Captain's sidearm
 * Destabilizer
 * Drone cannon
 * Drone cannon Ex-B
 * Firelance

Melee weapons:
 * Electro-suppressor
 * Shock baton

Ammo:
 * Alien power cell
 * Alien power module

Turret:
 * Alien turret - Turret which fire electric projectiles.

Vehicle mounted:
 * Death ray - Powerful cannon equipped on Mothership.

Robots and computers

 * Experimental weapons drone
 * Guardian drone
 * Support drone
 * According to its own records, the Skynet computer was created based partly on alien technology.

Vehicles

 * Alien ship crash site in California - A small saucer that housed 2 pilots.
 * Recon Craft Theta - Small alien vehicle, found in Capital Wasteland. Used by 1 pilot.
 * Mothership Zeta - Large alien vehicle located in space near Earth dedicated to study of humanity.
 * The Second Mothership - A ship of the same design as Mothership Zeta, it comes right after Zeta's Bridge is captured by the Lone Wanderer.
 * "Paladine" crashed craft.
 * Firelance Event craft - Identical vehicle to Recon Craft Theta, destroyed by unknown cause while near the Lone Wanderer.

Medical

 * Abominations - Beings created from humans as a result of alien experiment.
 * Alien biogel - Ingestible and curative gelatin-like liquid (Stated that they pour/rub it into injuries)

Miscellaneous

 * Alien epoxy - Alien repairing agent.
 * Alien homing beacon - A beacon teleportation sent by a Mothership to return quickly.
 * Alien squid food - A strange substance the aliens experiment on that can be used as food.
 * Drone control device - Remote control for drones.
 * Force field generator - Used for protective cover or blocking a passage.
 * Healing archway - Care generator in Mothership.
 * Inertia suppression field - Personal protection shield technology.

Behind the Scenes

 * The design of the aliens is similar to [Greys], a type of extraterrestrial commonly found in science fiction as well as UFO sightings and abductions.

Appearances
Aliens appear in Fallout, Fallout 2, Fallout 3 - Mothership Zeta add-on. and "Fallout: New Vegas"