Is there a fire alarm which detects smoke, heat AND CO all in one?
Try to work outside or a well ventilate area..wear gloves, safety glass's and mask: You can get a gel to remove the old stainfollow directions on the can..when I used it I applied it with a paint brush..let it sit then I took a putty knife and started removing the gel..wiping the excess on to old newspaper and paper towel. And when you put the stain on just follow directions on the can. +
it could be the humidity but it could also be dust. Get a can of air and blow them out. Carbon monoxide is a completely different tester. I've never seen one tied into the smoke alarms. Carbon monoxide alarms make a different beeping noise I believe. If you have a gas furnace you should def. have an C.M. alarm somewhere.