Unclear how this works but it sounds good: "Tremont Electric has created a kinetic energy-based charger called the nPower PEG (Personal Energy Generator). What's nifty about this charger compared to other kinetic energy harvesters is that it immediately converts kinetic energy to electricity and feeds it to your gadgets instead of storing the energy and then charging. The PEG can charge the average portable device up to 80 percent with an hour's worth of movement. What's better is that you don't need to strap the PEG onto yourself to harness the kinetic energy. It can be placed in your backpack or purse or strapped to your bike or kayak and derive the same energy. You can even use it while standing on the subway or bus."

just the buckle, not the belt