The T-Qualizer t-shirt has a built in sound sensitive graphic equalizer panel that lights up to the beat of the music. The battery pack is hidden discretely into a pocket inside the shirt. You can be the official sound check of the party for $
update: It appears that the Gadget Box has pulled the product from the site. Therefore, I changed the link to I Want One Of Those after a quick Google search.
update 2: Since the Gadget Box was the original link and we did copy the picture from their site, I have changed the link back to them.