Confusing? What was confusing? The guy in the research department of Wayne Enterprises develops basically a shield that reacts to the high frequency sounds of bullet shots. If you remember from the Batman Begins movie, it seems that, that department creates weapons and other things that are used by the military. (Batmobile was a type of tank that wasn't going to be used by the military after its development) So basically, Bruce sees it's potential as being useful for himself as Batman and takes it, signing it off from being used by anyone else. Everything else was just him having fun and being usual moral Batman.