The Security Droids were robotic drones which were created by an unknown species of aliens. When the aliens traveled to the Earth, their UFO crashed in Gravity Falls, Oregon. Whether the impact killed the alien crew of the UFO or not isn't clear, but the aliens were surely deceased by the 21th century. Despite this, however, the Security Droids weren't destroyed and remained active during all these years.
In "Dipper and Mabel vs. the Future," while both Ford and Dipper are searching the craft for some Adhesive to fix the Rift, they accidentally reactivate the security system. Dipper and Ford are then confronted by two Security Droids. Ford tells Dipper that they focus on adrenaline, and if you are not scared, they will not attack you. However, Dipper is unable to keep his fear in check, and one of the Security Droids attempts to blast him. Ford pushes Dipper out of the way, and shoots the droid with the magnet gun, but he is injured and captured by the other droid.
Dipper chases the Security Droid through the saucer. The droid puts Ford into a different, ship-like droid, programmed to take Ford to a prison at an unknown destination. As the ship prepares to take off through a hatch in the saucer, Dipper attaches himself to the ship with the magnet gun. The ship takes off, flying over the town and destroying the water tower as Dipper desperately tries to disable the ship. He uses the pulse option on the gun to disable the ship, which sends it crashing down in the woods. The remaining droid that survived arrives behind Dipper. He stands up to the Security Droid, yelling that he isn't scared and that nothing will take away his uncle, causing the droid to not detect any fear and disable itself.
The Security Droids of Crash Site Omega are metallic grey spheres with a marble-like pattern on their surface. On the direct front of them is an upside down red triangle, which is how they view intruders and scan for one's heartbeat.