You would be busted, too. Once such a device was operational and in use, it would be impossible to keep it secret. A simple check of your actual energy use from the grid against the projected energy use of your operation would get you forthwith.
I love you folks that say "it's not possible", as if you guys were privy to all the knowledge of the universe. That's a pretty ill-advised statement, considering the number of red faces in history of your spiritual brothers.
How in the world do you know what you don't know? Do you think that all possible advances in technology have been made to date and none remain?
I am willing to concede that there might someday be a whole new view of the universe and physics. However, I will state that given the current state of affairs it is impossible, and that every jerk who says he has a new perpetual motion machine, but of course won't tell us how it works, should just be ignored.