Installing speakers in a helmet often involves modifying the comfort liner or the protective EPS liner itself. Neither is an ideal solution, since the first method can affect the helmet's fit and the second its safety. A company called Tunebug has come up with what it believes is a better way—instead of putting speakers in your helmet, turn your helmet into a speaker.
The Tunebug Shake connects to audio devices using Bluetooth, and the Vibe uses a standard 3.5mm plug. Both are designed to be attached to a helmet, the shell of which is then "excited" by the sound generated by the unit, causing it to act like a speaker. The Shake and the Vibe apparently can be quickly and easily switched from helmet to helmet so you can enjoy your tunes while riding your motorcycle, bicycle, skateboard, or snowboard.
For more on both units, see Tunebug's website here.
(Note: I have not tested this product, nor have I received any compensation from the manufacturer for including it in a Product Spotlight. I just thought it was interesting/innovative/clever enough to warrant bringing it to your attention. All specifications and claims for the product are the manufacturer’s.)