Extreme weather alerts will soon be available in the palm of your hand.

Millions of smartphone users will begin receiving text messages from a sophisticated government system warning of dangerous weather and other emergencies.

The alerts are free and you don't sign up to get them. They're automatic.

Warnings are location-based, so if you're traveling, you'll receive an alert for whatever emergency is happening in your area.

The message will cause late-model smartphones to sound a special tone and vibrate.

Those who prefer not to get the warnings can opt out of the system.