Why, I'd take and by-pass the safety switch on the microwave oven. Hear someone moving around, just plug in and wait for the smell of "long pig" wafing through the air...it will go through the walls, so can be positioned in a closet, ceiling, on a night stand aimed at the bedroom door, or can be used to quiet down the "upstairs" neighbor...1200 watts should just about do it. No noise, no ballistics, no flash, and when the police came, I might offer them some hot, coffee, fresh out of the microwave oven!
There are some other materials which I could manufacture, but there is enough "grief" in the world without letting everyone read some simple, but deadly, readily available materials...