A crash course in changing the world.
Sound energy is generally very small in scope, so is not often thought of as an alternate energy source, but hopefully this won't sound too terribly silly. After all, my proposal is to power something very small with the sound from a highway. Sound energy could conceivably be used to turn the noise from the road to something helpful instead of pollution. There are people who live near airports and busy roads that could capture sound energy from sensors... hypothetically. The energy captured would be quite low, naturally, so the most it could be used is in areas where there is a lot of noise, and for electronics that were small and easy to charge, but it would have the effect of making the noise a little more useful (and perhaps then somewhat tolerable) to the people that live near it.
Besides, it might make karaoke nights a little bit more fun, to see who can produce the most power in a night!