In the event of a national emergency, a Presidential WEA alert would be issued at the direction of the President and/or his/her designee, and activated by FEMA.
link: https://www.fema.gov/news-release/2018/10/02/nationwide-emergency-alert-test-planned-oct-3-test-messages-will-be-sent
Yep. Every 3 yrs there will a test. What’s next? Yawn