The people who brought the nation the ominous announcement, “This is a test of the Emergency Broadcast System,” are working on an alert system for disasters that could ultimately send messages simultaneously to millions of cellphones nationwide. The first steps to building the system, called the Digital Emergency Alert System, were displayed on Wednesday in a television studio near Washington, where federal officials used a Public Broadcasting Service network to transmit a message by satellite to a television set and a satellite radio receiver. Full Story