Pumba - You set it for certain counties and types of weather. Like I have mine set for the county north of us(because lots of our bad weather comes from north moving south), the county I live in and the one immediately to our east, because we are actually only about 7 blocks from there. lol. So when a watch or warning is issued I immediately get the alert. It lets of a horrid alarm that would wake the dead and then you push the button for the alert. So like a tornado warning(which means one had been seen forming or had touched down) went off like an hour and a half ago for hendry county, but it was past us already. That way if you are sleeping and there is going to be a tornado, you will know and can get somewhere safe. We got it after those tornados in Orlando a few years ago when so many people were hurt because it came at night and no one knew it.
It can also be set for flood, snow(LOL), brush fire, and a million other things.