If a carbon containing substance (coal, oil, gas, wood) is properly burned, with high temperature and plenty of oxygen, mostly carbon dioxide forms. But if an appliance isn’t burning properly, due to either insufficient temperature or insufficient air mixing, more carbon monoxide will form instead.

Although you’re correct that older, poorly maintained appliances are a higher risk, even brand new appliances have sometimes been found by researchers to emit carbon monoxide. The detector will give you some peace of mind that your appliances are burning properly. Even if your appliances are burning properly, the detector will be handy in case someone accidentally leaves the oven on overnight, or a boneheaded house guest misuses the stove to heat the place, which could cause harmless trace levels of carbon monoxide to build up to a hazardous level.

Although it takes a relatively high dose of carbon monoxide to kill you, it’s colorless, odorless, and a relatively low dose can incapacitate you and make you unable to get away from the danger. That’s why we call it the "quiet killer". The detector will alert you well before you get too sick to escape. So relax, carbon monoxide poisoning is preventable, but remember to change the battery!