Real Evil Genius Manner - A big computer that will launch nukes all over the world which has deactivation right next to it for the hero's easy accessibility.
For Real - A retina scanner, thumbprint scanner, and series of seven keys that I have hidden around my lair in seven separate safes would turn on a computer, which would administer a voice check before asking for a 20-digit code. Then a DNA test would be given using my blood. The computer would turn on and I would double-click on Doomsday Device Controls, type in another password, tell my hackers to broadcast me over all the world's television stations on every channel, then say "You called me mad! I'LL SHOW YOU WHO'S MAD!! MUA HA HA HA HA HA HAA!!". Then, as the world watched in terror, I would fire my pre-destruction strike, which would set off fireworks all around the world. "You will go off in a bang!" I will say, then a nuclear device would hit every capital in the world, plunging it into chaos, and then I would rule the world and everyone would be forced to bow down to me! I would have other nuclear devices to use when I am close to death. When I go, everyone joins me!