You have seen nothing yet brother =/
Yup I've seen alot. I once mastering martial art and can sense "Jin" (Arabic name for spirit/demon/ ) they had several gate on our world. They dont require any human technology to come but indeed require human coorporation to interact (exorcism , paranormal activity). They dont look like what in picture, in our dimension, and can shape what ever they want, what you see a ghost actually just a "Jin" imitate the people who is already dead. They just a normal creature, some of them are Muslim, Cristian and Jews, pagan, and Lucifer worshiper even some are atheist. They can produce like human (although not the same characteristic ). It's look like nonsense but if you come to my country a lot of people is still able to do this. They are live among us in bad, celling, on roof, in toilet and they can see us but only small of people who can sense their existent.