It's called the NOAA Weather Radio network, and it's provided as a public service by the Department of Commerce's National Oceanic and Atmospheric Administration. The NOAA Weather Radio network has more than 480 stations in the 50 states and in Puerto Rico, the U.S. Virgin Islands and U.S. Pacific Territories. National Weather Service forecasters provide routine weather programming all the time to help you plan. The radios also send out a special alarm tone to alert you to a life-threatening situation. Sometimes, weather can turn deadly very fast.
Tornadoes are the best example.
Tornadoes may strike when people are sleeping or unaware of the forecast. With the NOAA Weather Radio, you will be alerted to dangerous weather with time to take shelter. NOAA Weather Radios broadcast more than just warning about natural hazards. They also broadcast warnings and information and technological disasters, such as chemical releases or oil spills. Every house should have a NOAA Weather Radio - just the way all houses should have a smoke detector.