At the appointed time, a Federal Emergency Management Agency (FEMA) office in Washington will broadcast to "primary entry point" television and radio stations "live code" for an Emergency Action Notification – the same code the president would use in an actual emergency. Other Emergency Alert System (EAS) stations will then get the message and broadcast it, in a cascading effect.
IN PICTURES: US natural disasters of 2011
There are 14,000-plus broadcast television and radio stations, as well as 10,000-plus cable television systems in the EAS.
The EAS uses a "daisy chain" approach in which a few dozen television stations relay their signals to secondary stations, which in turn relay their signals to others. One advantage to such a system is that it isn't likely to get clogged, like cellphone networks often do during emergencies, as they did after the 9/11 attacks.
But will this system, a holdover from the cold-war era, really work?
Today's EAS system is a direct descendant of CONELRAD (Control of Electromagnetic Radiation), a military alert system created in 1951. Then in 1963, after the Cuban Missile Crisis, the Emergency Broadcast System (EBS) was created by expanding the military system to include state and local governments. Finally, the system was upgraded and automated in the 1990s, and its name was changed to the Emergency Alert System.
The purpose of the test Wednesday, federal officials say,
is to put that old system through its paces – to allow FEMA and the
Federal Communications Commission (FCC) "to assess how well the
Emergency Alert System would perform its primary function: alerting the
public about a national emergency."