Basically, we don't have a warning system anymore, because the pieces that are left are mostly being dismantled (sirens, tv and radio) and all they seem to want to replace it with is an app that doesn't reliably work when the network is fine.
Lets be honest, if catastrophy should strike here, we would be last to know.
And then the whole radio clusterfuck. AM radio got totally torn down years ago to "cut costs", there's always discussions to dismantle plain old FM radio too and only serve DAB+ instead, which doesn't have nearly the buildout level compared to plain old FM radio.
I'm sick of this shit. Three decades and all what we had went down the drain. It's the same for coronavirus response - back in cold war times we had massive rolling stockpiles of everything, especially of PPE... but again, it all got eliminated to "cut costs".
AM even more so, although AM transmitters can be really power-hungry if you want to cover an entire country with one of them.
East Germany had a fully working siren network as well. And it was tested every Wednesday at 1pm.
What would you use it for? And why would having one that worked over AM or even FM be worth anything? People don't buy those radios any more. What difference does it make?
What you're describing sounds like a massive white elephant that was probably worthless even in the cold war. A proverbial safety blanket.