I understand that, but wouldn't a pattern generator that selects from a series of pitches and a larger series of patterns produce sufficiently unique enough items to ensure that the probability of overlap to be virtually null?
It's just a thought, like I'm against the whole thing in general, but it seems like this is doable without needing a lot of support
The point is that the audio pitches aren't outside human detection and don't have distinct enough patterns right now. Changing pitch and patterns would require appliance manufacturers' support, at which point you might as well go with mature, well-defined and well-implemented solutions, such as WiFi connectivity, rather than defining and implementing your own protocol based on audio pitches and patterns.