The EAS is a national public warning system that provides the President with communications capability to address the nation during a national emergency. The test is made available to EAS participants (i.e., radio and television broadcasters, cable systems, satellite radio and television providers, and wireline video providers) and is scheduled to last approximately one minute. The test message will be similar to regular monthly EAS test messages with which the public is familiar.
https://breaking911.com/heads-up-nationwide-emergency-alert-system-test-planned/