In my Port St. Lucie house, as of mid-September 2026, the reflex when a carbon monoxide alarm chirps is to reach for a battery. Put in a fresh one, hear the noise stop, and get on with the day. I understand the appeal. A battery is a small problem with an obvious fix; the alarm itself is easy to forget once it goes quiet.
Here in Florida, I have had to unlearn enough northern-house logic to pause at that point. A chirp can mean the battery is low, but an alarm can also reach the end of its service life. Those are different problems. The fresh battery may be exactly what a low-battery chirp needs. It does not make an old sensor new.
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What the CDC says
The CDC puts the replacement instruction plainly: “Replace your CO detector following the manufacturer’s instructions or every 5 years.” That is a direction to replace the detector, not merely the battery inside it. The CDC also recommends checking detector batteries in spring and fall. I read those as separate chores: pay attention to the battery, and pay attention to the age of the alarm…