I'm in a part of the country where we have frequent tornadoes. We even have tornado "season", generally in the Spring. The entire area has sirens, that are specifically designed to go off in the event of a tornado. The intention is to warn you that one is in the area, so you have enough time to seek shelter. It's not uncommon to be woken up in the middle of the night and have to go to the basement. I've never seen one, but they've come close. The damage they can do is astounding.