Is Twitter really the official way to notify people of danger? Or is there also a cell phone warning system?
Folks in SF that want to sign up for the texts can do so here: http://sfdem.org/public-alerts
Alert About Missile Bound for Hawaii Was Sent in Error, Officials Say https://news.ycombinator.com/item?id=16140761
There has been some controversy about the timing and use of WEAs for evacuations for the big wildfires in California recently, but I imagine it's hard to balance alarm fatigue with the need to warn people.