Carbon Monoxide Detector Beeping? What the Chirps Mean

Single chirp every 30-60 seconds: low battery

This is by far the most common reason people search for "carbon monoxide detector beeping." A single, short chirp every 30 to 60 seconds means the battery is running low and needs to be replaced. It's the same behavior as a smoke detector — the detector is telling you it can't reliably monitor for CO without a fresh battery.

This chirp is not an emergency, but you should replace the battery as soon as possible. A CO detector with a dead battery cannot protect you. Carbon monoxide is odorless and colorless — without a working detector, you would have no way to know it's present until symptoms appear.

Other CO detector beep patterns

• 4 beeps, pause, repeat — Active CO alarm. Emergency. Get out and call 911.
• 1 chirp every 30-60 seconds — Low battery. Replace the battery.
• 1 chirp every 15 seconds — End-of-life on many models. The detector itself needs to be replaced.
• 3 chirps every 15 seconds — Malfunction on some First Alert models. Try resetting the unit; if it persists, replace it.
• 5 chirps every minute — End-of-life on Kidde models. The entire unit needs replacement.

CO detector chirps sound identical to smoke detector chirps

Here's what makes this especially confusing: CO detectors and smoke detectors use the same type of piezoelectric buzzer, which produces a chirp in the 2,500-4,500 Hz range. The low-battery chirp from a CO detector sounds virtually identical to the low-battery chirp from a smoke detector. If you have both types in your home — and most homes do — you genuinely cannot tell them apart by sound alone.

This means the challenge isn't just "which detector is chirping" but potentially "is it my smoke detector or my CO detector?" The only way to know for sure is to find the specific unit that's making the noise.

Finding which CO detector is chirping

CO detectors suffer from the same localization problem as smoke detectors — the high-frequency chirp bounces off surfaces and is almost impossible to pinpoint by ear alone. WhichBeep solves this by using your phone's microphone to measure the chirp volume at each detector. Walk to each unit, let it record a chirp, and it will tell you which one is loudest — identifying the source objectively.

Battery types for common CO detector brands

• First Alert CO400/CO605 — 2 AA batteries
• First Alert CO710 — Sealed 10-year lithium (non-replaceable)
• Kidde KN-COB-B-LPM — 2 AA batteries
• Kidde C3010 — Sealed 10-year lithium (non-replaceable)
• Nest Protect — 6 Energizer Ultimate Lithium AA batteries
• Hardwired models with backup — Typically 9V backup battery

When to replace your CO detector

CO detectors have a shorter lifespan than smoke detectors. Most manufacturers recommend replacement every 5 to 7 years. The electrochemical sensor inside degrades over time and becomes less sensitive to carbon monoxide. Check the manufacturing date on the back of the unit — if it's older than 7 years, replace the entire detector regardless of battery condition. Sealed-unit models with 10-year batteries are designed to be discarded when the battery dies, since the sensor will have degraded by then anyway.