Sonoff RF Bridge with smoke/CO alarms

I have been looking for a solution to monitor battery-powered smoke/CO alarms within HA. Initially I thought about getting some Fireangel WiSafe devices along with their WiSafe relay, to hook it up to an ESP8266 running Konnected or something similar. It actually works out as quite an expensive solution and doesn’t allow activation of the alarms from within HA.

An alternative solution might be to use a Sonoff RF Bridge with Tasmota, and connect some 433MHz alarms to it. Has anyone tried this or have any idea which detectors might be compatible?

I guess the reason it turns out quite expensive is the cost of the relay and alarms? They are stated to work on 868MHz so might be possible to communicate with them without the relay?