I used to be a firefighter, and yes, could be CO. We sold CO detectors at cost to the townsfolk and they have saved more than a few people over the years. Every home should have a couple. Especially if they have an attached garage or gas heat.
I have three CO detectors in my home. My wife’s good friend and former employer died at 98 from CO. Sad. Even though I have three, I believe I got dosed (perhaps below threshold for alarm) with CO once. I felt groggy and had just started on a new pain medication (since discontinued) for arthritis. I left work and went to the doctors. I pulled a young female out of the rotation, who sent me to an ophthalmologist. As the day went on I began clear up and the ophthalmologist seemed to think I was a malingerer. The heating system was due for routine cleaning and the technician said it was cracked and leaking. I mentioned this to my regular GP at my next regular check up, but the episode has stuck with me.
Everyone should know that those detectors need to be completely changed out every few years. We replace ours every 5-10 years.
Re: Gas Heating.
We were in a rental house a few years ago that had a self contained A/C & Gas Heating Unit (like for a Mobile Home Unit) and the firebox had rusted through and I had been smelling unburned Natural Gas in the house when the A/C was running.
As We had Gas Stove/Oven, Water Heater and Clothes Dryer I had started the process of finding the source of the Natural Gas smell and after eliminating all of those options the Water Heater was vented well and it was in the Laundry Room in the corner.(both the Stove/Oven and the Dryer were brand new, purchased when We moved in to the house.) I decided that the source had to be A/C & Heater Unit.
I knew that the landlord was going to say it’s not his equipment so I called the Gas Company and asked them to come and check it out. I was correct that it was the house unit. So I got the landlord on the phone while the Gas Company Rep was there and let them talk directly to each other.
The landlord,of course still was in denial and had to call “his” HVAC Guy who came out and concurred with Myself and the Gas Company Rep. Even then the landlord wanted to just turn off the gas supply valve to the HVAC unit until winter started. Luckily his Guy sold him a new unit by telling him that the new unit was going to cost more the longer he waited to do it.
I HATE CHEAP landlords !!!