I have a carbon monoxide detector... 15 months ago it went off whilst I was cooking. turned out that the gas cooker was faulty and the rings producing large amounts of carbon monoxide. ironically it was not the detector that triggered my thoughts that something was wrong, it only confirmed what the problem was. my asthma suddenly started playing up and I was looking for the problem when I saw that the carbon monoxide detector was flashing red - not sounding the alarm though. I remember picking it up off the top of the cabinets and bringing it closer to me, that triggered the audible alarm.
I spent the night in A&E and it took months for some of my speech to come back - I could fully understand people, I could think words, I could just not get the words formed in my mouth to say them. Full recovery from that took well over 6 months and I have to say I was lucky....
Otherwise I am a live & learn person... don't worry too much about safety - it is often over done (like the signs along my local converted railway line, that warn there may be rabbit holes!) but when it comes to poisonous gases that you can't smell or see, you do need to be careful!