You know, as a parent and the husband of a teacher, I don't have a problem with this. How is it an invasion of privacy? You're at school for goodness sake, what is so private about that? So, somene can see if you're in the bathroom, is that a big deal? If you're in a classroom, you walk out of it in front of 20 or so other people who know where you're going!
Actually, I think this is a great idea. In theory it would keep kids from cutting class or leaving the campus. Only problem I see with it is it would be super easy to fool. "Hey, Joe, I'm cutting English to drive over to my girlfriend's house, take my tag." Still, you could still take attendence manually and avoid situations like that. Maybe I see things differently because I went to a High School campus that was laid out like a small college. It was literally sprawling and some buildings were a half mile apart and you had to dodge 2999 other students to get to class. I see the badge tracking system as a miracle at a campaus like that.