Carbon Monoxide Detector Beeping? What Each Beep Means

Carbon monoxide has no color and no smell. The CDC says more than 400 Americans die each year from unintentional carbon monoxide poisoning not linked to fires. More than 100,000 visit an emergency department, and more than 14,000 are hospitalized. Treat the 4-beep pattern as real until a responder tells you otherwise.

1. Get everyone outside to fresh air, pets included. Do a head count at the door.
2. Call 911 from outside. First Alert’s instructions say to stay in fresh air until the responder has arrived and the home has been aired out (First Alert support).
3. Watch for symptoms. The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion. It also warns that people who are sleeping can die before they have symptoms.
4. Do not go back in until emergency responders say it is safe (Kidde).
5. If it sounds again within 24 hours, First Alert says to call a qualified appliance technician to check fuel-burning equipment. It also says to make sure no vehicle has been running in an attached garage.

After 911, call your gas utility. These are the lines each company publishes for a carbon monoxide call or a gas emergency:

• PSE&G

  1-800-880-7734

  Emergency Service line, to have your appliances inspected after a CO alarm (source)

• New Jersey Natural Gas

  800-221-0051

  Listed on its CO page for after you have called 911; gas leaks go to 800-427-5325 (source)

• New Jersey Poison Control Center

  800-222-1222

  Listed by New Jersey Natural Gas for carbon monoxide information (source)

• PECO (Bucks County, PA)

  1-800-841-4141

  Gas emergency line, 24 hours a day (source)

Numbers as published on each company’s site on October 30, 2026. Call the utility that supplies your gas.

A beep is the loud alarm horn. A chirp is a short sound that means the alarm needs attention. First Alert’s support pages draw the same line: chirps are shorter than alarm beeps. The table lists each pattern from the makers’ own documents.

• 4 quick beeps, a pause, 4 beeps, repeating

  Kidde and First Alert

  Means: Carbon monoxide detected

  Do: Get everyone outside, then call 911

• 3 loud beeps, repeating

  First Alert smoke and combination alarms

  Means: Smoke or heat detected (fire alarm, not CO)

  Do: Get out and call the fire department from outside

• 1 chirp about every 60 seconds

  Kidde and First Alert

  Means: Low battery

  Do: Replace the batteries with the type named on the alarm

• 1 quick beep every 30 seconds

  Kidde KN-COB-B-LP

  Means: Error or service condition

  Do: Replace the battery; if it continues, replace the alarm

• 2 quick beeps every 30 seconds

  Kidde KN-COB-B-LP

  Means: End of unit life (10 years after power-up), no longer detects CO

  Do: Replace the alarm now

• Chirping every 30 seconds, 7 years after power-up

  Kidde CO alarms (Kidde support page)

  Means: End-of-life warning

  Do: Replace the alarm now

• 3 chirps about once a minute

  First Alert

  Means: Malfunction

  Do: Breaker off 1 minute, clean, test; replace if expired

• 5 chirps about once a minute

  First Alert

  Means: End of life (or backup battery not activated on a new unit)

  Do: Replace the alarm; check activation on a new one

• One long, continuous squeal

  Kidde

  Means: Unplugged or loose from the outlet, or a malfunction

  Do: Reseat the plug-in unit; call Kidde if it continues

Sources: Kidde KN-COB-B-LP user guide, Kidde beeping support page, First Alert, First Alert chirp guide and First Alert alarm sounds, all opened October 30, 2026. Patterns differ between models; your alarm’s label or manual is the final word.

Kidde publishes its patterns in two places: a support page for all its CO alarms and a user guide for each model. We used the guide for the battery-powered KN-COB-B-LP and KN-COPP-B-LP.

• 4 quick beeps, 5 seconds of silence, repeating: the carbon monoxide alarm. Kidde’s guide says it repeats for as long as dangerous conditions exist.
• One quick beep every 60 seconds: low battery. The model with a display also flashes “Lb”.
• One quick beep every 30 seconds: an error. The guide says to replace the battery, and if the beep continues, the unit has malfunctioned. The display model shows “Err”.
• Two quick beeps every 30 seconds: end of unit life, ten years after it was first powered up. The display model shows “End”. Kidde’s guide says to replace it immediately because it will not detect CO in that state.
• Chirping every 30 seconds on an older alarm: Kidde’s support page says its CO alarms begin chirping every 30 seconds seven years after first power-up. That is an end-of-life warning. The same page says a chirp every 30 seconds can also mean a malfunction. It lists Kidde product support at 1-800-880-6788.
• One long, continuous squeal: a plug-in unit that has been unplugged or has come loose from the outlet, or a malfunction (Kidde support page).

A display model also keeps a peak reading. Kidde’s CO guide says the peak memory shows levels from 11 to 999 ppm. Levels below 30 ppm will not set off the alarm. Kidde says not to ignore readings above 30 ppm. That memory helps when an alarm went off while nobody was home.

First Alert’s support site, which also covers BRK alarms, is support.brkelectronics.com. Its chirp guide and alarm sounds page give these patterns:

• 4 loud beeps, repeating: carbon monoxide. First Alert says its alarm sequences are 85 decibels, loud enough to alert people who are asleep.
• 3 loud beeps, repeating: smoke, or rising heat on a heat detector. On a combination smoke and CO alarm, this is the fire alarm.
• 1 chirp about once a minute: low battery. Other causes on the same list are batteries facing the wrong way, a drawer left partly open, a pull-tab still in place, rechargeable batteries and corroded contacts.
• 3 chirps about once a minute: malfunction. First Alert suggests turning the power off at the breaker for one minute, cleaning the alarm and testing it, and checking whether it has expired.
• 5 chirps about once a minute: end of life. The Test/Silence button hushes it for about 2 days; after about 2 to 3 weeks it cannot be silenced. Replace an alarm over 7 years old. On a brand-new unit, 5 chirps can mean the backup battery was not activated.
• Random chirps: on hardwired units, First Alert says the most common cause is the electrical installation, and it recommends an electrician.

One detail catches many people out. First Alert notes that removing the battery or unplugging the alarm will not stop a low-battery chirp. Its fix is a fresh battery.

Some homes have a CO detector that is part of a monitored alarm system, not a stand-alone unit. These behave differently. First Alert’s chirp guide even warns that a chirp may come from another device, such as a security system, with a similar low-battery signal.

Here is one alarm-panel detector, as an example only: the 5800CO wireless carbon monoxide detector. The Honeywell 5800CO installation manual says:

“If a low battery is detected, the transmitter sends a low battery message to the control panel, which beeps and displays the detector’s zone number.”

In the same low-battery section, the manual says that after 7 days the detector’s horn chirps about every 45 seconds. A trouble condition or the end of its life also gives one chirp every 45 seconds. It also says to tell the central station before testing, because a test sends an alarm signal to the panel.

We name this model only to show how a panel detector behaves. It is not a list of what Security Dynamics installs, sells or monitors. Your own detector’s manual is the final word.

So if the house is beeping and you are not sure where from:

1. Look at the keypad first. A zone number or a low-battery message points to the detector on that zone.
2. Call your monitoring company before you test or remove it. A test can send an alarm to the central station.
3. Do not pull a hardwired detector off the wall with the power on. First Alert says to turn off the circuit breaker before you look at any wiring.
4. Use the battery your detector’s manual names. Kidde’s KN-COB-B-LP, for example, takes three AA batteries.

The rule for homes is in the New Jersey Uniform Fire Code. People often mix up the carbon monoxide rule with the smoke alarm rule, so here are both, from the code text.

• Which homes need CO alarms

  One- and two-family and attached single-family dwellings, except buildings with no fuel-burning device and no attached garage

  N.J.A.C. 5:70-4.19(d)

• Where CO alarms go

  In the immediate vicinity of the sleeping area(s)

  N.J.A.C. 5:70-4.19(d)1

• What kind of CO alarm

  Battery, hard-wired or plug-in, listed to UL 2034 and installed under NFPA 720; or a supervised CO detection system installed under the Uniform Construction Code

  N.J.A.C. 5:70-4.19(d)2

• Smoke alarms (a separate rule)

  On each level and outside each separate sleeping area; 10-year sealed battery alarms, effective January 1, 2019, unless the home has AC-powered alarms

  N.J.A.C. 5:70-4.19(a), (c)

• When you sell or rent

  The owner gets a certificate of smoke alarm, carbon monoxide alarm and portable fire extinguisher compliance before the home is sold, leased or changes occupants

  N.J.A.C. 5:70-2.3(a)

• State fee

  $45 more than 10 business days before the change of occupant, $90 at 4 to 10 business days, $161 under 4; a town with its own enforcing agency may set a different fee

  N.J.A.C. 5:70-2.9(d), (f)

What that means if your detector is beeping:

• A dead or expired CO alarm can hold up a sale or a lease. Under 5:70-2.3(c), no certificate is issued unless the home has a CO alarm meeting UL 2034, if the home has fuel-burning appliances or an attached garage.
• The certificate is not transferable. If the change of occupant does not happen within six months, the owner applies again. For a seasonal rental unit, the enforcing agency may issue one for up to 12 months.
• Replace with a listed alarm. Look for UL 2034 on the box or label.
• Bucks County homes follow Pennsylvania rules, which this guide does not cover.

Code text read on October 30, 2026 from the Legal Information Institute’s copy of the New Jersey Administrative Code. The enforcing agency for your town issues the certificate and can confirm the fee.

PSE&G says carbon monoxide poisoning is most likely to occur in the winter. These are the winter sources the utilities, the CDC and First Alert point to:

• Portable generators after an outage. The CDC says never to use one inside a home or garage, even with doors and windows open. Run it outside, more than 20 feet from windows, doors and vents.
• Snow and ice over vents. PSE&G warns that snow, ice, nests and leaves can block appliance vents and cause CO to build up.
• A car or snow blower warming up in an attached garage. PSE&G says CO can drift from the garage into the living space.
• A furnace, boiler or water heater that is not burning cleanly. New Jersey Natural Gas says gas equipment should have a clear blue flame. A yellow or orange flame may mean a problem.
• Using a gas oven to heat the house. PSE&G and the CDC both say never to do it.
• Wind and weather. First Alert’s false alarm guide lists high gusty winds, temperature inversions and the negative pressure from exhaust fans as causes of on-again, off-again CO.

The CDC also says to have a qualified technician service your heating system, water heater and other gas, oil or coal appliances every year. Have the chimney checked or cleaned every year too. When you run a generator, the CDC says to use a battery-powered or battery-backup CO detector in the home.

A stand-alone CO alarm only makes noise inside the house. That is fine when someone is home. It does nothing for a shore house that sits empty all winter, a rental between tenants or a parent’s home while they are away.

• A monitored detector reports to a central station. Our home fire and smoke monitoring adds monitored smoke, heat and carbon monoxide detectors to an existing system. Our home alarm systems include carbon monoxide monitors with fire department dispatch.
• The state code allows it. 5:70-4.19(d)2 accepts a supervised carbon monoxide detection system installed under the Uniform Construction Code as an alternative to single-station alarms.
• A peak-level display helps after the fact. Kidde’s peak memory shows the highest reading since the last reset. You can see if CO rose while you were gone.
• Check the house before the season. The CDC says to check CO detector batteries when you change the clocks each spring and fall.

We serve Mercer County, Bucks County and our Ocean County service area. A business with a CO concern can start with commercial fire alarm monitoring.

1. Make sure it is a chirp, not the alarm. If you hear 4 beeps and a pause, stop here, get out and call 911.
2. Count the chirps and match them to the table above. Two beeps every 30 seconds on a Kidde, or five chirps a minute on a First Alert, means replace the alarm. A battery will not fix it.
3. Check the date on the back. First Alert says to replace an alarm over 7 years old. The CDC says to replace a CO detector following the maker’s instructions or every 5 years. Kidde’s KN-COB-B-LP has a label on the side for the “replace by” date.
4. Fit fresh batteries of the type printed on the alarm. Check that they face the right way, the drawer is shut and any pull-tab is out. First Alert says rechargeable batteries can cause chirping.
5. Press the test button and listen for the 4-beep test pattern. Kidde’s guide says a working alarm plays 4 quick beeps, 5 seconds of silence and 4 quick beeps.
6. Hardwired unit still chirping? Turn off the breaker before you look at wiring. First Alert lists the electrical installation as the most common cause of erratic chirps.
7. Check where it is mounted. Kidde says to install CO alarms at least 15 feet from fuel-burning appliances. First Alert says 15 to 20 feet, because an alarm too close can go off from brief, local CO.
8. On an alarm system, call the monitoring company before any of this.

Never leave a CO alarm without batteries to stop the noise. For a wider routine, see our security system maintenance checklist.

Sources for the answers above are linked in the sections above.

Related Services and Guides

• Home Fire & Smoke MonitoringMonitored smoke, heat and carbon monoxide detectors tied to a 24/7 central station.
• Home Alarm SystemsBurglar, fire and carbon monoxide detection for New Jersey and Pennsylvania homes.
• Security System Service in NJService and repair for the alarm system your detectors report to.
• Monitored Fire Alarm Systems GuideHow a monitored fire alarm differs from alarms that only sound in the house.