During the Cold War, it was pretty common to see and hear tests of the Emergency Broadcasting System. Unlike those alerts, phone users can not opt-out, or disable, their phones from receiving the message.
Three New Yorkers filed a federal lawsuit last week attempting to block the test, saying it violates free speech and is an unconstitutional seizure of electronic devices.
The Wireless Emergency Alert system is used to warn the public about unsafe weather, missing children, and other critical situations through cell phone alerts.
"Users may opt out of receiving alerts in the imminent threat and AMBER categories but can not opt out of receiving Presidential alerts", the agency said.
It's just a test, but don't try to opt out of receiving it - there's no way to stop the alert from popping up on your phone or television screen.
FEMA officials said the administration can only send such an alert for national emergencies or if the public were in peril, rules outlined in a 2006 law.
He said some people did not receive alerts on some devices during that test.
The test will take place on Wednesday, October 3, 2018, at exactly 2:18 PM EDT. Those who did not receive the message may have been on a phone call or had their phone turned off, for example.
The alert was initially scheduled to occur September 20, but FEMA spokesman Mark Peterson said the test has been postponed, and Wednesday was the alternate date for the test. It will supposedly read "THIS IS A TEST of the National Wireless Emergency Alert System".
For the WEA alert, you'll get a push alert (pop-up message box) on your phone, and the alert will also include a tone and vibration.
This is a test of the nationwide alert system to warn the public about unsafe weather, missing children and other critical situations, and you may notice that your phone makes a different notification sound to normal.
A survey by the National Center for Health Statistics showed that in the first half of 2017, more than 52 percent of all households in the United States had only wireless cellphones, according to the U.S. Centers for Disease Control, or CDC.