You actually have to opt-OUT of these alerts on almost any modern smartphone made in the past 5-6 years.
I had to “hack” my phone to disable them (using the term loosely; you need to connect it to the computer and use a terminal).
Disabled them because in my country, they abuse the system and send all alerts at the “Presidential” level (aka. top priority and everyone might die unless you do something soon). My phone manufacturer helpfully decides not to have Presidential alerts respect my volume settings (like Do-Not-Disturb).
I also live in a particularly large region.
All this combined means that I have to live without alerts that say “Tornado incoming” because I don’t want monthly alarms blaring in the middle of the night to tell me that a child is involved in a custody dispute somewhere about a 7 hour drive away from me. Guess they wanted me to keep my eyes open and call the police when I see a “white vehicle” because it may contain the “missing” child, whose entire description is “7, last seen wearing a red shirt and jeans”.
So yeah, I opted out. Against all alerts, against my will.
Also, in my country, when there was an active mass/spree shooter who was masquerading as a cop and pulling people over before shooting them, they DIDN’T use the emergency alert system. They used Twitter. Remember to like and subscribe!