My wife has a small shop, and she plays free licensed music. She can't legally play her own music when people outside of the family circle are present in the shop. How can I automatically switch music when someone enters? I was thinking of some bluetooth door detector and some custom software, but can't seem to find either. I'm a software architect/dev and can write it if necessary, but I'd prefer to use some existing solution. Any ideas on good hardware and software for this?