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 Federal Emergency Management Agency (FEMA), in coordination with the Federal Communications Commission (FCC), will conduct a nationwide test of the Emergency Alert System (EAS) and Wireless Emergency Alerts (WEA) on September 20, 2018. The WEA portion of the test commences at 2:18 p.m. EDT, and the EAS portion follows at 2:20 p.m. EDT.

https://www.fema.gov/emergency-alert-test