You receive an emergency alert: "BALLISTIC MISSILE THREAT INBOUND. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL." What do you do? How do you think your neighborhood will react? What memes be on Lemmy?
My phone is usually dead, misplaced, or the volume is at 0%. So I would probably crack a beer and stand on the porch wondering why the neighbors are freaking out.
You will likely still hear the cell broadcast. Alerts of this level make every phone give off a piercing sound and even if your phone is dead, you will hear it from your neighbours' because it's loud.
If your phone and early warning systems support cell broadcasting you will still get notified. Cell broadcast alarms are always at full volume, regardless of your settings.
Same boat, after I got a series of very loud "flash flood" alerts going late into the night. Every time the timeframe was extended there was another alert. I did not fancy being woken up at 2 am in my second floor bedroom to a alert telling me to stay off the roads.