The way they describe it sounds scary (Matrix or something):
Thanks for not scaring people off of this. LOL.Scientists call such devices "parasitic" generators. Many of the most futuristic projects focus on harvesting the energy of crowds.
Interesting thing to think about: right now, electricity generation is very inneficient/low, but there are new advancements all the time in heat-capturing, magnetic-frictionless-motion, etc that may lead to good enough efficiency in the future to make this useful. What level does everyone think it would have to get to to be useful and could we ever get there?