The Emergency Alert System (EAS) is a system used in the USA and is described by http://transition.fcc.gov/pshs/services/eas/ as follows.

The EAS is a national public warning system that requires broadcasters, cable television systems, wireless cable systems, satellite digital audio radio service (SDARS) providers, and direct broadcast satellite (DBS) providers to provide the communications capability to the President 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 alerts and weather information targeted to specific areas.

Reddit user rtlsdr_is_fun is working on software to automatically detect an EAS broadcast from a NOAA Weather Radio stream using an rtl-sdr (or any SDR, or even an internet stream) and then immediately play it and record it. This will allow the EAS alert to be heard up to 2 minutes faster than email/sms alerts, without the need to constantly listen to the NOAA WX Radio.

He stresses that his software is still in the very early alpha stages, but you can read about his project on his Reddit post here, which also contains a download link.