Buy a new one, replace an old one.
Test all of them but realize that the testing doesn’t test the ability to detect CO, just the ability to sound an alert.
As I have mentioned in the past, due to my Carbon Monoxide poisoning a couple of years ago and having several CO detectors in the house (including next to the furnace) and them not going off because they had “expired” and getting very sick from it, I buy a new one and put it in my house every year so I know that I always have at least one that isn’t expired.
In the time that I started telling this story to people, I have heard at least 15 other stories about people who were similarly poisoned either at work or at home. I have also seen on the news several people who have died from it. This stuff is serious people. More serious even, IMO, than smoke detectors because CO is a silent killer and could be slowly killing you over days or weeks.
Once again…
CARBON MONOXIDE DETECTORS EXPIRE.
BUY NEW ONES BEFORE THE OLD ONES EXPIRE.
I moved into a townhouse from an apartment last month and one of the first things I did was buy another CO2 detector and thought about your posts. I got a decent one at Costco for a fair price.
The other thing I did is buy some fire extinguishers. Then I reached out to family and few friends and none of them had extinguishers either so I bought some of those too (again Costco saves the day)
Good advice as usual Joe.