Although I'm not exactly qualified-I might have some advice.
My younger brother has autism (high functioning) and I have Paranoid Schizophrenia. I suppose I'll try to mash the two of us together
My brother is a lot younger than your son, but also is always on electronics. Or rather he used to be. You could say his name over and over again and he would have no idea you were talking to him. If we made him turn on off his Xbox he would throw a fit. As with all Autism cases, patience isn't exactly your forte. A therapist suggested the complete opposite of electronics: books. At first we were rather skeptical-but it was a huge success. With Autism you're in your own world and video games is just one way of escaping. A book is another way. I know it may not be successful, but it's just an idea. If he's interested in a certain subject perhaps you could subtly give him a book. Make him think it's his idea to read it. Again just an idea.
Now on to the Paranoid Schizophrenia. With the medicine bit, I can relate to your son. It's not exactly "fun" to be on the medicine. You're not yourself and everything seems rather dull. At one point in my life I refused to take it and used to hide it so no one would know I wasn't taking it. It took a lot of coaxing to get me to take it again and in this aspect I can only wish you luck. As for your son walking in on you unannounced, it's quite possible he's baiting you. He may not be doing this on purpose. You are probably trying to explain to him that you can't just do that, and he probably presses for more. Remember the key word here is PARANOID. He really is paranoid about everything, or anyway that's how I am. He may even be looking for confirmation that he's right to be paranoid. Or right that the world is out to get him. Even deeper, he may be seeking your attention. Anyone with Schizophrenia does not have a firm grasp on reality. He may even be trying to confirm that he is REAL.
I know this may not have been what you have been looking for, I hope it helps. Also, does your son have a gameboy?