I’m also investigating how to setup an alarm system with homey (still in the early stages though). My thoughts so far:
- For the door/window sensor I’m looking at the new Aqara p2 sensor. These work via Matter over Thread. From what I’ve read Matter devices do not need dedicated apps, as long as they follow the correct standard.
- I’m probably going for a keyboardless setup. E.g. when the smart door lock is locked or all residents are set to away, set the alarm. Something along those lines.
- You could use indoor/outdoor Sonos speakers for alarm sound
Edit: I’m also looking into “when all persons are asleep, set the alarm”. The asleep part I could check here when all smartphones are connected to the upstairs wifi. But there are other ways as well (via Aqara FP2 sensors, when all phones are charging at night, …)
Just my 2 cents 
