There's only one invention which would definitely assure the death of the inventor and the supression of his device, and that's a time machine. Once such a device is invented and built and is out there in common usage, someone in the future who is unsatisfied with things would go back into his past and snuff you out. The future is a big place, and it will contain a lot of whackos (as does the present). Thus it is certain that someone will go back and obliterate the invention.
So, attic-dwelling weirdos, if you're working on a time machine, better watch out! Success will guarantee your doom. But if it's just a perpetual-motion machine, you're safe.
Just how would this thing work? If you "go back" in time, the earth has moved, space has expanded etc. etc. So the "way-back" machine may put you somewhere you don't want to be at a time of your choice. (i.e. it must be a time-space machine)
Hey, I thought the rules were that it had to be invented in a basement, not attic! :)