Last night we had a little scare. Our carbon monoxide detector went off around midnight - why does this only happen at night?!?? It was chirping 5 times (we now know that means "end of life" for the detector). We changed the battery, and the chirping stopped, but we weren't sure what it had meant. It wasn't the carbon monoxide alarm and it wasn't the "need a battery" alarm.
We have radiators as our heat source (which is a wonderfully efficient and comfortable way to heat your home), so that is our one combustible appliance in the basement. (We used to have a gas water heater too, which I dearly miss.)
We thought about just going to bed, but it seemed too risky. I mean, if we were wrong we might not be alive in the morning. Finally, we decided we would turn our boiler off and get a replacement detector in the morning. I had far more layers on, so I was chosen to go back down into our basement to turn off the boiler. I asked, "How will I be sure I turned it off?" Luckily, William marks equipment very clearly and I had no doubt when I switched "Boiler System Power" to off.
We bought a new detector first thing in the morning, and replaced the old one. As is always true, home repair projects take multiple trips to Lowes or Home Depot (having a general contractor in the family does not alleviate this national curse). After a few tries we had our new detector in and our boiler back on. To help us avoid this in a few years, we notated the expiration date on the detector. I always thought they were good forever, but apparently they are to be replaced every 5-7 years.
Luckily, we air sealed our basement last year, so our house wasn't horribly cold after 8 hours with no heat.