I wonder why they don't have these things in Tornado Alley? It’d be good for those heavy sleepers. If they did re-instate them, the alarms would probably have the 520Hz square tone; not in Code 3, of course.
If memory serves correctly, the carrier current signal can't pass through transformers, so it's only good for a local building or block basically.
we have sirens in most areas, and a lot of major cities have speaker arrays now so instructions can be announced after the sirens have ended. add to that most cell phones receive weather alerts now, even if you don't want them, i think we are pretty well covered.