Recent improvements in how the National Weather Service (NWS) defines warning areas have resulted in significantly higher accuracy and smaller warned areas, compared to the decades-old county-wide warning method. http://www.nws.noaa.gov/sbwarnings
The WeatherCall® system continuously monitors the National Weather Service's NOAA weatherwire. Using computerized mapping (GIS) the system compares a subscriber's specific location to the location of the warning area. When a severe weather warning includes your location, you will receive a phone call from Chief Meteorologist Matt Laubhan, 24 hours a day. You can also receive the warning by email with a detailed map of the threat or by SMS text messaging.
Matt Laubhan explains how WeatherCall works