I have written yet another Home Assistant alarm system for voice intents called 'Voice Alarms'.
I looked at some existing integrations like HA-Alarms-and-Reminder and HA-Clock but found them too complicated and lacking documentation. So, like a true programmer, rather than spend a couple of hours working out how they worked, I wasted two weeks and wrote my own. Initially based on HA-Clock but greatly simplified. It simply exposes the triggered alarm to a binary sensor that you can use to trigger your automations to whatever siren, SMS, media player, flashing lights, etc. you want to use.
I use the built-in timer alarm sounds within the M5Stack Atom Echo and HA Voice preview firmware to trigger my alarm sounds.
This can be done by exposing the internal switch that triggers the timer sound to Home Assistant (see voice alarms).
This is the first integration I've written (cut and paste, AI, Google), so please, any feedback would be useful.