Another follow-up: In October 2024, the first one started beeping due to low battery. I can see that the battery level reading actually dropped from 75% in January to 50% in April. Apparently it cannot show less than 50%, so the battery level readout is not too good, but considering that the battery has lasted more than 4 years, I am quite pleased.
Hey I was looking at smoke sensors too recently. I’ve found out that Bosch smart home has one and it’s zigbee and compatible with zigbee2mqtt. Not sure if the standard openHAB zigbee can also chew that.