Halo smoke alarms cost $129 each while regular smoke and CO detectors cost about $35. My house has 5 or 6 of them, I integrated them to ST for $43, see this post
I just did that for about $43 in my house. I’m in the US but they all work the same.
Smoke / CO detectors have 3 wires, neutral and hot for power and a common wire to trigger the other detectors in the house, it’s red in the US.
I used a $13 Kiddie smoke alarm relay like this one
and a z-wave dry contact like this one
On the relay you won’t use the gray and yellow wires for this application.
To one of the smoke detectors (I used my basement unit so I did not care about hiding the relay like I would inside the house), wire the black (hot) wire from the relay with the black of your smoke alarm system, the white from the relay (neutral) to the white of your system and the red from the relay (common trigger) to the red of your system.
Then wire the blue wire from the relay (common) a…