(Information Adapted from the FEMA website)

The Emergency Alert System is a national public warning system that requires TV and radio broadcasters, cable television systems, wireless cable systems, satellite digital audio radio service providers, direct broadcast satellite service providers, and wireline video service providers to offer to the President the communications capability to address the American public during a national emergency. The system also may be used by state and local authorities to deliver important emergency information such as AMBER (missing children) alerts and emergency weather information targeted to a specific area.

EASscreen

The FCC works with the Federal Emergency Management Agency and the National Oceanic and Atmospheric Administration's National Weather Service to implement the EAS at the national level. Only the President determines when the EAS will be activated at the national level, and has delegated the administration of this function to FEMA. Accordingly, FEMA activates the national EAS, and directs national EAS tests and exercises. The NWS uses the EAS on a local and statewide basis to provide the public with alerts and warnings regarding dangerous weather and other emergency conditions.

The EAS allows participating providers to send and receive emergency information quickly and automatically, even if their facilities are unattended. If one link in the system for spreading emergency alert information is broken, members of the public have multiple alternate sources of warning. EAS equipment also provides a method for automatic interruption of regular programming, and in certain instances is able to relay emergency messages in languages other than English.

Along with its capability of providing an emergency message to the entire nation simultaneously, the EAS allows authorized state and local authorities to quickly distribute important local emergency information. A state emergency manager can use the EAS to broadcast a warning from one or more major radio stations in a particular state. EAS equipment in other radio and television stations, as well as in cable television systems in that state, can automatically monitor and rebroadcast the warning.
Additionally, EAS equipment can directly monitor the NWS for local weather and other emergency alerts, which local broadcast stations, cable systems, and other EAS participants can then rebroadcast, providing an almost immediate relay of local emergency messages to the public.