This is almost never actually the case. Your daily keys are random, so the only way to know it's you is for someone to monitor bluetooth devices near by, and as

This is almost never actually the case. Your daily keys are random, so the only way to know it's you is for someone to monitor bluetooth devices near by, and associate those keys with a physical identity... which becomes very difficult unless there's only one other person you come into contact with. In practice, it provides about the best anonymity you could ask for.