Equipment, technology, people and training are all needed.
California has had its fair share of disasters in recent years. Most being wildland fires with some entering into urban and suburban housing areas. In those circumstances you need a robust warning system with multiple means of issuing warnings.
See this article in Government Technology magazine on multiple issues around emergency warnings, Next-Generation Emergency Alerts — What’s Working Where?
The article highlights the fact that you need multiple warning systems. Many an emergency management agency has hung their hat on the purchase of a commercial system. The downside to that is the fact that people have to "opt in" for the system to get the warnings. I estimate that only a relatively small percentage of the community's population actually are participating, 10-15 percent perhaps.
I would not use it as a primary method, but using social media channels to augment the formal warning systems would be a great idea that some have adapted to their warning procedures.
At the end of the article, it is noted that one community got authorization for more staff to dedicate two additional FTE just to work on warning programs. For those of you who are the one-armed paper hanger emergency manager doing all phases of emergency management by yourself, that is likely out of reach. The only hope is that after the big disaster and everything falls apart, your successor will be given more resources. Bummer, I know!