I read this book when I was in high school...the cover had, I believe, a young boy standing in front of a silver sphere and there might have been a young girl leaning against a lamp post in the background. It was about this kid (young boy) who was taken away to this other world, I believe, where machines weren't allowed. The "police" were these huge silver spheres. This kid meets a young girl who takes this thing (I think it was a watch or a calculator) that he snuck in and with it she took over one of these silver spheres. Later in the story the young boy is left in the wilderness and somehow ends up thinking he's an animal/alien thing. Sorry this is so vague. I've been looking for this book for years and it's getting foggier each day!