The test, which will begin at 11 a.m., will be broadcast for 30 seconds with emergency tones on TV and radio, as well as cable and satellite TV systems.
Southlanders will hear the message "This is only a test."
The alert has been used locally during earthquakes and life-threatening weather warnings, but there has never been a nationwide test.
"It'll be in many ways like any other test that people have heard on the radio or seen on TV, but this time it'll be on every channel, every radio station, at the same time," said Jamie Barnett of the Federal Communications Commission.
The emergency alert system is designed to enable the president to address the nation in the event of an emergency.
"It's never been activated - the Cuban Missile Crisis, 9/11 - nobody's ever felt the need to really activate it," Barnett said. "You can't really trust what you don't test and that's why it's important for FEMA and for FCC to do this, because we do anticipate that there will be glitches. We want to find the glitches and make those better."
The test will not affect cellphones usage.
Officials originally planned for the test to be three minutes long, but they were concerned that could cause unnecessary panic and a large number of calls to 911.
The Associated Press contributed to this report.