Hello, thanks for showing the inside of this device. I'll try to clarify the situation.
This sensor is most likely based on TuyaMCU, more specifically TuyaMCU for battery powered devices. https://developer.tuya.com/en/docs/iot/tuyacl...niversalserialaccessprotocol?id=K95afs9h4tjjh
The MCU runs all the time and controls the CB3S power supply. CB3S is only enabled when status needs to be reported. The MCU via UART (the same as for programming, i.e. TX1 and RX1) reports data to CB3S via the TuyaMCU protocol, and when the WiFI module forwards them, the MCU turns it off again.
TuyaMCU reports variables described as dpID + type + value, you will have to guess what dpID means. Probably the smoke detection status will be 1 or 0 and type bool, and e.g. battery level type enum (or value?) and values 0, 1, 2 and 3.
These types of devices are supported by OpenBeken, but to be sure, first capture UART packets, baud is 9600 or 115200, you can use RealTerm and then analyze them in TuyaMCUAnalyzer: https://www.elektroda.pl/rtvforum/viewtopic.php?p=20528459#20528459 https://github.com/openshwprojects/TuyaMCUAnalyzer
Then you need to write autoexec.bat for OBK where you map dpID to channels and give them meanings (channel types), HASS discovery should work in this case (it was improved at the beginning of May).
Then you need to upload OBK, here is also a bit of fun, because the MCU will turn off the WiFi module and block the UART line, so you must probably cut the UART paths and connect your own power supply ...
And that's how it should go.
As related materials, it is worth recommending these topics, here I remotely started at @DeDaMrAz
the humidity sensor on TuyaMCU: CB3S/BK7231N] Temperature/humidity sensor with TuyaMCU - Diagram, reverse engineering
Here I was running the door sensor on TuyaMCU: Energy-saving (?) battery door/window sensor for WiFi DS06
I recommend trying to run it as part of sports, quite a lot of work has already gone into supporting this type of device so maybe it will go smoothly.
PS: There is always an alternative - throw out the MCU and if the smoke detector with the hardware (I didn't analyze it in depth) shows 0 or 1 digits then it can be done on OpenBeken itself just like the door contact without the MCU (use OBK deep sleep and pin wake).