I don't mind. If the microphone is in use it means that there is an active call, so I have to tell the server that it must lower the volume of music. I don't want to register anything. The very important thing is that I don't want to keep polling the mic status, because the app could be in background or closed. I need to react to some sort of O.S. event that says "Hey, microphone is in use!" or "Hey, the microphone is no more in use!"