An Emergency Alerts Systems (EAS) test usually happen during television or radio broadcast, in case of an widespread disaster or terror attack.
Today the U.S. government, and the Federal Emergency Management Agency (FEMA), sent out more than 200 million mobile device alerts across the nation as part of a nationwide test of the Emergency Alert System and Wireless Emergency Alerts.
"THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed.”
Although the text is called the "presidential alert," the President doesn't actually write it. The system is ran by the FEMA, which says all of the country's major cell phone carriers participate.
"The President will not originate this alert, say, from his mobile device," a senior FEMA official told reporters. "You would not have a situation where any sitting president would wake up one morning and attempt to send a particular message."