The Obama administration will conduct the first nationwide test of the country's emergency alert system Wednesday afternoon.
The system would be activated by President Obama in the event of a terrorist attack or other major disaster.
State and local authorities have used the alert system to warn people of severe storms, child abductions, and other life threatening emergencies.
William Craig Fugate, Federal Emergency Management Agency administrator, explained that the test, scheduled for 2 p.m., is an "opportunity to check and make sure our systems are working across the country if we have a national emergency."
FEMA has been publicizing the test on its website. It will be seen and heard on all television and radio stations, and all text-based alert systems.
Officials made it clear, however, that Americans will still be able to use their cell phones during the test.
"If this is a system that is going to assist in getting the public timely information during a significant event, it is going to help first-responders because the public is going to have more information available to them, be more informed," said Capt. Mark Savage, with the Los Angeles County Fire Department.
"It might reduce panic," he added.
Since the system has never been tested nationwide, the Department of Homeland Security said Wednesday's drill will be important in determining whether the system will work in case of an actual national emergency.