Fahey just wrote up the Guitar Hero Air Guitar Rocker, but I scored a little hand-on from the CES show floor.
The belt buckle senses your air rocking (via magic pick) and sends the signal to an accompanying belt pack that both acts 1.) as the speaker and 2.) allows you to switch between 5 preloaded songs. I tried Black Sabbath's Iron Man on for size—that's not me in the above video for good reason—because I found that while the song could be played back at variable speeds depending on strumming tempo, I often unintentionally double-strummed (aka, looked like an even bigger douchebag than had I been rocking out to more "traditional" air guitar on the CES floor).