Everything Jeanne said is spot on. The tornado sirens are really mostly outdated now, but small towns still have them, and some communities even in bigger cities. Areas that have the sirens have multiple sirens placed around so as many can hear as possible. We have sirens in my town and one is just a few blocks from my home. We aren't just "Tornado alley" of the west or even of the U.S., we are Tornado alley of the world!