I don't see why the ring itself couldn't be tapped at checkout in the very same manner as a phone/tablet. Logistically, with the right internals this shouldn't be a problem, and would provide the ideal solution.

I don't see why the ring itself couldn't be tapped at checkout in the very same manner as a phone/tablet. Logistically, with the right internals this shouldn't be a problem, and would provide the ideal solution.