First, I don't think Twitter has the competence to do this - they're barely functional now. For instance, they threw away their infra for identity validation, so how will they figure out who needs access to the klaxon button?

Second, Twitter is shedding users like a husky in the desert. As someone above said, if nobody see it, who cares?

Third, there is already an emergency alert notification system for cell phones. Building another one just provides conflicting signals in an emergency.

Twitter is dude's blog now. Pretending it is good for anything other than servicing his ego will result in frustration and waste.