siren stopped working

Everything has been working fine for nearly a year. Now the alarm won't sound. Everything else still works fine, like the lights turning on, text alerts, etc.

I have checked that the alarm is still physically connected. Any ideas?

This was me being dumb. I had moved the ST hub into a new "IoT LAN" that I had created. It's odd that other things were still working, but I believe this was the core issue.