Carbon Monoxide Detector Beeping? What Each Sound Means

A carbon monoxide detector that beeps is either warning you about carbon monoxide or telling you about itself. Four loud beeps in a repeating pattern, or a steady alarm, means leave the house and call 911. A single chirp every 30 to 60 seconds usually means a low battery. Two chirps often means end of life.

The sound matters. A CO alarm cannot be treated like a nuisance smoke alarm, because carbon monoxide has no smell or color. This guide helps you tell an emergency from a battery warning in under a minute.

What do the beeps on a carbon monoxide detector mean?

Patterns vary by brand and model, so your manual is the final word. The common ones look like this:

Seattle Fire advises calling 911 if the alarm is sounding continuously without stopping, and Kidde notes that its alarms signal end of life with a repeating chirp and, on digital models, an END message. If you are not sure which sound you are hearing, treat it as an emergency until you know otherwise.

What to do first when the alarm sounds

1. Check for symptoms. Headache, dizziness, nausea, confusion, or feeling sick that gets better when you leave the house.
2. Get everyone out. Include pets. Move into fresh air outside, not just another room.
3. Call 911 from outside. Say that your carbon monoxide alarm is going off.
4. Do not go back in. Wait for firefighters to test the air and clear the home.
5. Get medical help if anyone feels unwell. Carbon monoxide poisoning needs a doctor.

Where does carbon monoxide come from?

Anything that burns fuel can make it. The usual sources in a home are:

• A furnace or boiler with a cracked heat exchanger or a blocked flue. If your furnace is short cycling, see furnace keeps shutting off.
• A gas water heater, stove or dryer that is poorly vented.
• A fireplace or wood stove with a blocked chimney.
• A portable generator run too close to the house, in the garage, or on a porch. Generators should run outdoors and well away from windows and doors. If you need one, the generator sizing tool helps you pick the right size.
• A car left running in an attached garage.
• A grill or charcoal burner brought indoors.

If the power is out and you are heating with anything that burns fuel, read our power outage checklist first.

Why is my CO detector chirping when there is no emergency?

If the pattern is a single chirp and nobody feels sick, one of these is usually the reason.

1. The battery is low

This is the most common cause. Replace the batteries with fresh ones of the type listed in the manual. Many chirps start at night because the room cools and battery voltage dips. Press and hold the test button for a few seconds afterward. A loud alarm means it works.

2. The alarm has reached end of life

If the chirp continues after a new battery, the alarm is probably expired. Kidde states that a CO alarm does not detect carbon monoxide once it is in end-of-life mode, so replace it. Look for a date on the back. Most units last about 7 to 10 years.

3. The battery is not seated or the door is not shut

Open the compartment, remove the batteries, and press the test button once to drain any charge. Put the batteries back, check the direction of the plus and minus signs and close the door firmly. Some models chirp when the battery drawer is not fully closed.

4. A fault or dust in the sensor

Dust can trigger a fault. Gently vacuum the vents with a soft brush attachment. Do not spray cleaner into the alarm.

5. A power problem on a hardwired model

A hardwired alarm with a backup battery can chirp after an outage or a tripped breaker. Check the breaker, then replace the backup battery.

Can I just press the hush button?

Some models have a hush feature that quiets a chirp for a while. It does not fix anything. Seattle Fire notes that the chirp returns when the silence period ends. Use it to get through the night, then fix the cause the next day.

How to replace a carbon monoxide detector

1. Turn the old alarm counterclockwise to remove it from its mounting plate.
2. If it is hardwired, turn off the breaker first and disconnect the plug connector.
3. Buy a new alarm that has a recognized safety listing on the package.
4. Mount it the way the manual says. Many manufacturers advise placing alarms on every level of the home and near sleeping areas.
5. Write the install date on the back or on a sticker.
6. Test it monthly.

Combination smoke and CO alarms are common. If yours is one of them, the chirp pattern may differ for each hazard. See why is my smoke detector chirping for the smoke side, or smoke detector going off for no reason.

When to call a professional

• The alarm sounds and someone feels sick. Call 911.
• The alarm keeps going off after you replace it. A new alarm that sounds again is a real signal. Call your gas company or an HVAC technician to test the appliances.
• You see soot, scorch marks or a yellow pilot flame around a furnace, water heater or stove.
• You smell gas. Leave, then call the gas company from outside.

Many utilities and fire departments will check for carbon monoxide at no cost when you call. Ask when you phone.

What not to do

• Do not remove the battery and leave it off.
• Do not ignore a chirp for weeks. An alarm in end-of-life mode is not protecting you.
• Do not paint over an alarm.
• Do not use a gas oven or stove to heat the house.
• Do not run a generator or a car inside a garage, even with the door open.

Bottom line

Learn the sound. Four beeps or a continuous alarm means get out and call 911. A single chirp means check the battery. Two chirps or END means the alarm is at the end of its life and needs replacing. If you are unsure which one it is, treat it as an emergency.