No doubt free energy devices have existed for decades using many different technologies, but all the inventors get killed or mysteriously disappear, have their labs raided and are arrested on all kinds of bullshit charges.
One of my favorites is hydrogen production from water in excess of what conventional science deems possible for the required input energy.
Here is the best demo of a generator running by electrolyzing its own water… Bet you never saw one powered up in an elevator before.
youtube.com/watch?v=cMlciNOyo_U
Awaiting more info about the method here before I go and buy a 3D printer though!