I usually listen to Mac output through headphones, which I keep plugged in almost all the time. I'm happy to have speakers squelched. But there are some alerts--e.g. message coming in from IM, or notifications from a web page, that I'd like to hear about if I'm across the room.
Is there any way to separate some audio signals from others? Certain notifications I wan to play over the speakers, even if the headphones are the primary output. If this is not feasible through the standard audio system, is there some sort of USB or wireless audio or visual notifier device I could purchase? I don't need full stereoscopic audio quality for this--just something to indicate "notification has come in" when the sound is not otherwise audible.
I'm using a MacBook Pro, 15", 2011 version if that matters.