The alert test, which is FEMA's first for the wireless emergency system - and is being coordinated with the Federal Communications Commission - will sound similar to an Amber Alert or flood watch warning.
Cell towers will also only broadcast the alert for about 30 minutes, so if you're on the phone or out of range for a half hour after 2:18 p.m. ET, you might miss it.
Here's what you'll see on TV or hear on the radio: "THIS IS A TEST of the National Emergency Alert System".
Cellphone users can not opt out of the test, which uses the same special tone and vibration as AMBER alerts and tornado warnings.
WEA was technically launched in April 2012, but this will be the first time FEMA has tested the system on the presidential level in hopes to work out the kinks, the agency said this week. This will be the fourth nationwide test of the EAS after similar tests in 2011, 2016, and 2017.
In 2006, President George W. Bush signed an executive order to create an effective, reliable, integrated, flexible and comprehensive system to alert the American people in situations of war, terrorism, natural disaster or other hazards of public safety and well-being.
Tomorrow - Wednesday October 3 - your phone will receive a text message; assuming you're in the United States, that is, and use Verizon, T-Mobile, AT&T or Sprint as your carrier. Those who did not receive the message may have been on a phone call or had their phone turned off, for example.
This is the only planned test of the EAS and WEA as of now, but that could change depending on the results of Wednesday's test.
You can click on the "Related Link" with this story to go directly to FEMA's website with additional information about what to expect.
He said some people did not receive alerts on some devices during that test. "No action is needed", it'll read.
The test message will have a header that reads "Presidential Alert", according to the agency.
That's the first thing you should know about the test of the national emergency system that will send an alert to almost every phone in the country on Wednesday. Others will not. No action is required.