It takes energy to move.  Move to the kitchen, to school, to the couch.  And there is a lot of energy that can be captured from these movements.  Maybe you have a pair of those sneakers with the lights?  They capture the energy from walking and uses it to power a few tiny light bulbs.  Now scientists are trying to take it to the next level by developing more sophisticated nanodevices and make them cheaper.  They use these things called piezoelectric crystals.  Piezoelectric things have been around since the mid-18th century but these new ones are printed and they can be printed onto flexible materials that are also biocompatible.  So maybe you don’t want them stitched to the bottom of your feet but perhaps they can be stuck onto a lot of different things making energy for all sorts of devices. No more need to change the battery unless you become a couch potato.
http://tinyurl.com/ygbr3g3
read about the original science http://pubs.acs.org/doi/abs/10.1021/nl903377u