Every phone in Israel got a special message when missiles from Iran were fired. No application, no nothing, just by the virtue of being connected to to an Israeli phone cell tower (it worked even on imported phones)

My understanding that it is a standard feature, this is how earthquake warning works in Japan.

Point being there is no "hacking" involved. Standard feature

Basically a modern version of leaflets.

With all that being said, I'd consider that a gross misuse of emergency functionality.