The system also sends out AMBER alerts and warnings about extreme weather or other local emergencies. The alert won't have any substantial content - it's just a system test - but this sets a whole new precedent for how Americans are informed.
"When those messages appear on mobile devices, people should take those extremely seriously", Antwane Johnson, director of the IPAWS system, told CBS News.
The presidential alert can only be activated by the current president, but the reasons for doing so are legally defined. It has grown more sophisticated since it was created in the 1950s, and now includes a system to send warnings to cellphones, too. But the best-case scenario is that no emergency ever happens that's serious enough to warrant a nationwide phone alert.
And although it wasn't Trump himself sending this alert from his mobile device (alerts will be sent from a FEMA official), a lot of Americans on Twitter treated the pilgrim message as if it were straight from the president.
FEMA is required to test and maintain alert systems and says the aim is to "assess the operational readiness of the infrastructure for distribution of a national message and determine whether improvements are needed".
The message will go out to all working phones compatible with the WEA System.
The text paves the way for future high-level "presidential" alert that would be transmitted in the event of a nationwide emergency. President George W. Bush authorized presidential alerts in 2006, but one has never been sent before Wednesday.
A number of people are testing ways to turn off the presidential alerts through jailbroken or rooted phones, but these methods may bring risks of causing other problems with your phone.
A subsequent investigation by the Federal Communications Commission found that the staffer responsible for the message had thought an attack was truly underway, having misinterpreted a drill.
This message and will be labeled a "Presidential Alert" and, yes, will be coming at the direction of the White House. And although you can opt out of AMBER alerts and weather alerts, you can't opt out of Presidential alerts.
Legislation about emergency alerts have been rising since 9/11.
During a real emergency, tune in to KNIA/KRLS for more information. It hasn't said yet whether the test went well.
The law establishing the alert says it can not be sent out for any reason other than "a natural disaster, act of terrorism or other man-made disaster or threat to public safety", according to NowThis.