Pelty is kind of amazing, and is most definitely going on my Zombie Apocalypse Survival List. Pelty is a Bluetooth speaker powered by fire.
How it works: Thermodynamics and a little thing called the Peltier effect. The Peltier effect basically means that electric current is created when electrons move from one material to the other with the help of temperature differentials. So basically, science.
This will go great with my handcrank phone charger.