said by cornelius785 :

sure the microwave may use 1200W, but how much actaully gets out into the room? probably not alot considering the magnetron (the device that radiates the microwaves) is kept in a small (or large) metal cage that in theory, no microwaves leak out, in reality, only a small amount leaks out probably (don't know exactly, so look it up if you're interested). if it wasn't in a metal cage, well some funky (electronic devices freak out) or deadly (literal cooking of yourself) stuff will be happening.