I guess, but in my experience, the scarier encounter is when I'm on a busier road and all of the sudden one of the cars is much closer to me than the others. I'm used to riding in traffic (if I couldn't get used to that, I couldn't ride in my area) so having cars come up behind me is something I get very used to. It only becomes a problem when one comes much closer to me than it should. And I don't think this thing would differentiate those, would it? I mean, if you're saying that it has a way to differentiate a car that's going to pass you with three feet to spare vs. one that's going to pass with, say, one foot to spare then I totally agree that's worth having. But if it can't, it doesn't address my need - I don't need cars to even obey the four foot law. I just need them to reasonably give me some clearance. Three feet is plenty. One foot leaves no margin for error. I want to know about the ones that are going to be a foot or less away from me. I don't need to know about anyone else, but if this thing beeps for anyone within coming up behind me, it's going to lose its impact pretty quickly and I won't pay attention to it.