Fireplace and carbon monoxide

don't confuse/mix up CO2 with CO

Yep, completely right. Sorry.

Assuming the corresponding saturation in the room air, it only takes a few breaths until fainting. Oxygen deficiency usually manifests rather as sudden tiredness – nothing hurts, smells strange or anything like that.

CO detectors are not that expensive, IIRC, we once had one in the apartment with an (old) gas floor heating system. It is important to replace them regularly (7 years?). In case of doubt, the chimney sweep will advise.

yes pure horror... maybe they fell asleep and then didn’t wake up...

where would you install such a co2 detector? I don’t need the chimney sweep for that, do I?

can someone recommend one to me?

I have now also ordered two CO detectors. I chose ones from Binwo. Two pieces for 23 euros. You’re not supposed to take cheap ones, but from what I found in a Google search about the detector, it always performed just as well. This is explicitly my opinion.

They should be installed in every room with a fireplace and in the bedroom, I have read. Also at least two meters away from the fireplace and installed at a height of 150 cm.

where would you place such a CO2 detector

CO, not CO2 ;-). We had it in the hallway. The gas boiler was in the kitchen, with the children's room and bedroom branching off from the hallway. This was coordinated with the chimney sweep at the time. The detector is mounted on a wall (not on the ceiling).

CO detectors should be installed, in my opinion, as low as possible.