Today's test will also reach TV and radio at 2:20 p.m. EDT.
Twitter user Ed Krassenstein posted a graphic which read: 'Presidential Alert: The Clintons are coming! "No action is needed". That means if your wireless service is provided by one of the more than 100 carriers that participate in the WEA system-and most cell phones are WEA enabled-you just have to sit back and let it be.
In January, after months of escalating exchanges between Mr Trump and North Korean President Kim Jong Un, the state's emergency personnel sent out an alert message reading, "BALLISTIC MISSILE THREAT INBOUND TO HAWAII".
The system was created in 2008 and activated in 2012.
The buzz and tone have the same feel and sound as those used for the Amber and weather alerts.
More than 100 mobile carriers are participating in the program, the agency said, meaning almost all cellphones will receive the alerts.
"Oh my. A "Presidential Alert" emergency". "You would not have a situation where any sitting president would wake up one morning and attempt to send a particular message".
Then who pushes the button?
FEMA officials use a device that's "very similar to a laptop computer", the senior FEMA official said. Some people reported not getting the alerts or getting them on a delayed basis.
Can I silence my phone or turn off the alert? After all, phones continually send and receive data both when we're using the phone and even when we're not.
US restricts visas to unmarried gay diplomats
Most diplomats affected come from countries where same-sex marriage is legal, another official said, without providing numbers. And unmarried partners who aren't yet in the United States will not be eligible for visas to move there.
FEMA will still test the EAS a few minutes after they sent out the WEA. Some got as many as four alerts on their phones; others didn't get any.
What about the other screens in my life?
Not everyone was pleased about the decision to send out the test alert.
"Now you know you say presidential alert and some people are thinking, 'Aw man, I see President Trump sending out Twitter messages all day long".
The first test of the national wireless emergency system by the Federal Emergency Management Agency is shown on a cellular phone in Detroit, Wednesday, Oct. 3, 2018.
An mobile phone screenshot of the Emergency Alert send by FEMA to all U.S. mobile user to test the National Wireless Emergency Alert System, Oct. 3, 2018. The other option is to keep your phone from connecting to a cell tower.
"When those messages appear on mobile devices, people should take those extremely seriously", FEMA's Antwane Johnson told CBS News correspondent Anna Werner.
The test seemed to go off without a hitch.
No matter what you were doing or where you were, everyone got the same alert. Older models that are not WEA-capable will not.
A number of iPhone users on AT&T's network - including this reporter - did not receive the notification until they had rebooted their smartphones.