Well. Aliens are Demons.

However, I would draw a distinction. Biblically there is a difference between "demons" and "fallen angels".

Demons are disembodied half-human half-angel spirits of the nephalim who were the result of angelic fathers and human mothers in Genesis 6. They all perished in the flood, and being neither human nor angel, they have no place to go to, neither heaven nor hell. These are the "extra-dimensional" beings people interact with when using things like DMT, altered states of consciousness, demonic possession (as they have no body of their own). They cannot appear to people.

Fallen angels are.. well.. angels (a class of created non-human intelligent beings) who are disobedient to God, ie Satan, those angels who came down in the day's of noah (those now locked away in "Tartarus"), and all the other angels who followed in Satan's rebellion still free at this time. Like obedient angels, they are generally non-corporeal, but have the ability to take on a physical manifestation (but it would seem they are not "allowed" to, as the last fallen angels to do so were confined by God in chains of darkness until the Judgement). Angels and their disobedient counterparts are on the order of millions in their number, and are responsible for the rise and fall of nations, the upholding of physical laws, weather, celestial phenomenon, to name a few. In those aspects, we see the "war in heaven" between good and evil. Evil nations vs good nations, violent weather, the "powers being shaken" in terms of miraculous events.

Fallen angels, given their ability to manifest visually/physically, may account for the vast amount of "UFO/UAP" sightings. However, I think that some of what we see as UFO's are actually a poorly understood human attempt to create their own version of fallen angelic technology using information obtained from both demons and fallen angels at sites like Area 51. Basically, they gave us the blueprints, we built them, and have no fking idea how they work.

food for thought.