This Wednesday, November 9, at 2 pm eastern standard time, every TV broadcaster, cable channel, radio station, and satellite radio program from Puerto Rico to Missouri to American Samoa will be interrupted for 30 seconds by the federal government. Don't panic—there's no nuclear strike. But if there were a nuclear strike, this is how the feds would spread the word.

It's the first-ever nationwide test of the Emergency Alert System (EAS), which hopes to provide key information immediately to all Americans in the event of a truly national emergency. This national system will look and sound much like the current (and local) emergency warnings often seen on TV or heard on radio, but the scope is larger and it can be put under the direct control of the President. The Federal Emergency Management Agency (FEMA), the Federal Communications Commission (FCC), and the National Weather Service (NWS) will all coordinate the test, but it's FEMA that actually transmits the alert code.

Concerned that such a test might alarm people, the agencies are going to extraordinary lengths to provide a heads-up. I first heard about the test in an e-mail newsletter from my city government, which told residents last week, "Do not be alarmed when an emergency message will take over the airwaves this is only a test." The test will display a warning message on TV screens, though as my city helpfully noted, "Due to some technical limitations, a visual message indicating that 'this is a test' may not pop up on every TV channel, especially where people use cable to receive their television stations."

But not to worry! Though such warning messages might look terrifyingly real, they will eventually feature an audio message explaining that this is just a test. The government is still concerned that hearing-impaired users, in particular, might mistake the test for a real alert. The FCC has produced a series of brief ads to notify people about the test, and cable operators have taken to warning people about it on their monthly cable bills (which everyone reads, right?).

So what's so special about November 9th at 2pm? FEMA has the answer. "November 9 is near the end of hurricane season and before the severe winter weather season begins in earnest," says the agency, "The 2:00 PM EST broadcast time will minimize disruption during rush hours, while ensuring that the test occurs during working hours across the United States."