The message is scheduled to be the first trial of the "Presidential Alert" system, a new way to notify Americans across the country of national emergencies.
We've had 56 National Emergencies since 1980, 28 of which are still in effect. George W. Bush declared 13 emergencies and Barack Obama declared 12 — nearly all of which are still active today. Bill Clinton declared 17 national emergencies, six of which are still active. Ronald Reagan declared six and George H.W. Bush declared four — but all of those have been revoked by now. https://www-m.cnn.com/2017/08/12/politics/national-emergencies-trump-opioid/index.html
I definitely want to opt out since none of them needed my immediate attention. Unfortunately, that's not an option. Yet I can opt out of local alerts which often do need to get to me right away (amber alerts, weather warnings, etc)