Carbon Monoxide Detector Beeping? What the Chirps Mean

One chirp a minute: low battery

This is by far the most common reason people search for “carbon monoxide detector beeping”. Kidde documents the CO low-battery signal as “chirping or beeping once every 60 seconds”.^[1] One short chirp, roughly a minute apart, means the battery is going and needs replacing.

It is not an emergency, but it is not something to leave either. A CO alarm with a dead battery cannot protect you, and carbon monoxide is odorless and colorless — without a working alarm you would have no warning at all until symptoms appeared.

One chirp every 30 seconds: end of life, and the sensor has already stopped working

This is the pattern most worth knowing, because it is the one people mistake for a battery. Kidde: “Seven years after initial power up, a Kidde CO alarm will begin chirping every 30 seconds. The chirp will not stop until the unit is powered off, and it's vital to replace the carbon monoxide alarm immediately since it can't detect CO when it enters end-of-life mode.” ^[1]

Read that last clause twice. An alarm chirping every 30 seconds is not a nuisance you can silence and deal with at the weekend — it is a unit that has stopped detecting carbon monoxide and is telling you so. Where the cause is end of life, a fresh battery will not bring it back. If the alarm has a digital display, Kidde says it “will show an ERR or END error code”.^[3] Kidde also notes that a 30-second chirp can point at a malfunction rather than end of life.^[1] Where it is a malfunction, the model's own manual may ask for a battery before a new alarm: on both Nighthawk models below, Kidde's troubleshooting table says to replace the three AA batteries first and to replace the unit only if the beeping carries on.^[11]

Other CO detector beep patterns

Count the chirps over a full minute rather than over a few seconds. The signals differ by how many chirps land in a minute — and by who made the unit. A pattern that means end of life on a First Alert does not mean the same thing on a Kidde.

• 4 beeps, pause, repeat — Active CO alarm. Emergency. Everyone outside into fresh air, then call 911 from outside.^[1]
• 1 chirp every 60 seconds — Low battery on a Kidde CO alarm. Replace the battery.^[1]
• 1 chirp every 30 seconds — End of life, or a malfunction. On end of life the sensor has stopped detecting CO, and Kidde says to replace the alarm immediately. For a malfunction Kidde asks you to call its support line instead, and sends error codes to the model's own manual.^[1] Check that manual before buying anything: on both Nighthawk models below it asks for fresh batteries first.^[11]
• One long, continuous squeal — Kidde lists this as a tamper-resist warning or a malfunction, not a CO reading.^[1]
• 3 chirps a minute — Malfunction, on First Alert models. First Alert's own manuals give this as three chirps every minute, not every 15 seconds, and say the alarm needs replacing.^[4] A fresh battery will not clear it.
• 5 chirps a minute — A First Alert signal, not a Kidde one: end of life or low battery, depending on the model.^[5] No Kidde document we have checked describes a five-chirp pattern at all.

What these models document, model by model

The model number is printed on the back of the alarm. If yours is one of these, its own manual beats any general rule — and on both of them a 30-second beep means two different things depending on whether you hear one beep or two.^[11]

• One quick beep every 60 seconds on a Kidde Nighthawk KN-COB-B-LP (three AA batteries, no display) — The batteries are low. Replace all three AA batteries.^[11]
• One quick beep every 30 seconds on a Kidde Nighthawk KN-COB-B-LP (three AA batteries, no display) — The unit is in an error condition and is not monitoring for CO. Replace all three AA batteries first; if the beeping continues, the unit has malfunctioned and must be replaced immediately.^[11]
• Two quick beeps every 30 seconds on a Kidde Nighthawk KN-COB-B-LP (three AA batteries, no display) — End of unit life, ten years after it was first powered up. Replace it; it will not detect CO.^[11]
• One quick beep every 60 seconds on a Kidde Nighthawk KN-COPP-B-LP (three AA batteries, digital display) — The batteries are low. Replace all three AA batteries immediately.^[11]
• One quick beep every 30 seconds, with "Err" on the display on a Kidde Nighthawk KN-COPP-B-LP (three AA batteries, digital display) — The unit is in an error condition and is not monitoring for CO. Replace all three AA batteries first; if "Err" continues, the unit has malfunctioned and must be replaced immediately. Pressing the Peak Level button while "Err" is showing gives an error code to quote to Kidde’s product support line.^[11]
• Two quick beeps every 30 seconds, with "End" on the display on a Kidde Nighthawk KN-COPP-B-LP (three AA batteries, digital display) — End of unit life. Replace it immediately; it will not respond to CO.^[11]

Both of these models also sound the CO alarm itself as four quick beeps, five seconds of silence, repeating — the same pattern as the emergency signal at the top of this page.^[11] More models go in here as their manuals are read.

CO detector chirps sound identical to smoke detector chirps

Here's what makes this especially confusing: the low-battery chirp from a CO detector sounds virtually identical to the low-battery chirp from a smoke detector. Both are a short, high, piercing tone at roughly the same interval, and neither Kidde nor First Alert publishes a frequency that would let you tell the two apart. WhichBeep listens between 2,500 and 4,500 Hz, but that is our own detection setting, not a manufacturer spec — it is where these chirps sit in practice, not a number any manual gives. If you have both types in your home — and most homes do — you genuinely cannot tell them apart by sound alone.

Plenty of units are both at once, which removes the question and replaces it with a worse one. First Alert's hardwired SC7010B is a combination smoke and CO alarm in a single housing.^[10] If a unit like that is the one making noise, the pattern is the only thing telling you which sensor is talking.

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 models

Only models we could confirm against the manufacturer's own product page are listed. If yours isn't here, read the label inside the battery door rather than assuming — the assumption is what sends people to the shop for the wrong cell.

• First Alert CO400 — one 9V battery. First Alert lists “Battery Size: 9V, Number of Batteries: 1”.^[6]
• First Alert CO710 — a built-in 10-year sealed lithium battery, listed as not replaceable. When it goes, the alarm goes.^[7]
• Kidde KN-COB-B-LPM — three AA cells, not two. Kidde's page gives it as “Battery Operated (3 AA's included)”, and lists the model as discontinued.^[8]
• Kidde C3010 — sealed 10-year lithium, never changed. Kidde: “10-Year Sealed-in Lithium Batteries”.^[9]
• Hardwired models with backup — Read the label, don't assume. First Alert's hardwired combination smoke/CO alarm SC7010B takes two AA cells, not the 9V most hardwired units of its era use.^[10]

When to replace your CO detector

The electrochemical sensor inside a CO alarm wears out, so the unit has a fixed life regardless of how the battery is doing. Kidde states that its CO alarms “have a proven life of seven to ten years, depending on the model type”, and draws the line at a single year: “As of 2013, all Kidde carbon monoxide alarms have a 10-year life” — with three named exceptions, models KN-COEG-3, KN-COPE-I and KN-COPP-3 — while an alarm made before 2013 has a seven-year life.^[3]

So the date on the back of the unit matters more than its age in the abstract. A 2012 alarm was finished years ago; a 2019 one has time left. Check the manufacture date, check it against your own manufacturer's stated life, and replace on that. Sealed models with 10-year batteries are built to be discarded when the battery dies, because the sensor has reached the end of its life by then anyway.^[9]

Sources

Every beep pattern and troubleshooting step on this page comes from the manufacturer's own documentation or a federal safety regulator. Where a manual contradicted us, we changed the page.

1. [1] Kidde. Why Is My Carbon Monoxide Alarm Beeping or Chirping? (retrieved 2026-10-02)
2. [2] First Alert. Installation & Reference Manual: SC5 Wired Smart Smoke & Carbon Monoxide Alarm, Model SMCO600NV-AC (retrieved 2026-09-06)
3. [3] Kidde. When Should I Replace My Carbon Monoxide Alarm? (retrieved 2026-09-07)
4. [4] First Alert. User's Manual: Wireless Interconnect Smoke Alarm, Model SA511 (M08-0194-005) (retrieved 2026-09-06)
5. [5] First Alert. User's Manual: Smoke Alarm, AC Powered with Strobe Light and 10-Year Sealed Battery Backup, Model SM110LED-AC (retrieved 2026-09-06)
6. [6] First Alert. CO400 Carbon Monoxide Alarm/Detector, Battery-Operated (retrieved 2026-09-07)
7. [7] First Alert. 10-Year Battery Carbon Monoxide Alarm with Temperature Display (CO710) (retrieved 2026-09-07)
8. [8] Kidde. Battery Operated Carbon Monoxide Alarm KN-COB-B-LPM (retrieved 2026-09-07)
9. [9] Kidde. Sealed Lithium Battery Power Carbon Monoxide Alarm C3010 (retrieved 2026-09-07)
10. [10] First Alert. Hardwired Combination Photoelectric Smoke and Carbon Monoxide Alarm with Battery Backup (SC7010B) (retrieved 2026-09-06)
11. [11] Kidde. Carbon Monoxide Alarm User's Guide: Models KN-COB-B-LP and KN-COPP-B-LP (retrieved 2026-10-01)