During severe weather, National Weather Service personnel interrupt routine broadcasts and substitute special warning messages. This tone will sound an alarm or automatically increase the volume in many receivers. Such receivers allow interested listeners to be alerted to warnings for their area even if they do not have the volume set at an audible level. NOAA Weather Radio has been the designated as the sole Government operated radio system to provide direct warnings into private homes for both natural disasters and nuclear attacks. You will need a Weather radio receiver that is either tunable or crystal controlled.
Weather radios are available in a variety of styles and prices.
The price is usually proportioned to the sensitivity and quality of the receiver. Other desirable features are a warning alarm, alternative power source, and a provision for an external antenna input connection. Here A list of weather radio stations across the United States can be found Here.