It's not possible to turn off alerts of the highest authority, "Presidential alerts", without turning off the phone. All basemodem and smartphone manufacturers selling in North America hardcode this into the black box part of the firmware. (Which is part of the approval process and why you'll never be able to buy a 'fully unlocked' phone.)
For example in Ontario, every alert is sent out at this authority.
For example in Ontario, every alert is sent out at this authority.