Why Is My Carbon Monoxide Detector Beeping? Alarm vs. Chirp, and What to Do

A carbon monoxide detector can make several different sounds, and they mean very different things. One is an emergency. The others are the alarm asking for a new battery or telling you it has reached the end of its life. Knowing which is which matters, especially in a Minnesota winter, when furnaces, water heaters and boilers run hard and houses are closed up tight.

Here's how to tell them apart and what to do for each. If you're reading this while an alarm is sounding a loud, repeating pattern, stop reading: get everyone outside and call 911.

A loud, repeating alarm: treat it as an emergency

A full alarm is loud and repeats in a pattern. On many CO alarms, including Kidde models, it's four short beeps, a five-second pause, then four more beeps, repeating. Some alarms also flash a red light or announce "Warning, carbon monoxide."

Kidde's own guidance in its beeping and chirping support article is to treat that pattern as an emergency until you know otherwise. Here's what to do:

• Get everyone, including pets, out of the house right away into fresh air.
• Call 911 from outside. If you have gas appliances, you can also call your gas utility's emergency line.
• Don't go back inside until emergency responders say it's safe.
• If anyone has a headache, dizziness, nausea, confusion or unusual sleepiness, tell the dispatcher. Those are symptoms of carbon monoxide exposure.

Don't silence the alarm and stay inside to figure it out. Carbon monoxide has no color or smell, and you can't rule it out by looking around. Once the house has been cleared, have the furnace, water heater, boiler and other fuel-burning appliances inspected before you use them again.

A single chirp every minute or so: low battery

A short chirp once every 30 to 60 seconds usually means the battery is low. It's annoying, but it isn't an emergency. Replace the battery with the type listed on the alarm, then press and hold the test button to confirm the alarm works.

Hardwired alarms have a backup battery too, and they chirp when that battery runs low. Some sealed alarms have a 10-year battery that can't be replaced. When that battery is done, the whole alarm needs to be replaced.

Chirping that won't stop after a new battery: end of life

CO alarms don't last forever. The sensor inside wears out, and most alarms are designed to warn you when they reach the end of their service life, typically somewhere between seven and ten years after they were first powered on. Kidde, for example, describes an end-of-life signal of one chirp every 30 seconds that won't stop with a new battery, and says the alarm no longer detects carbon monoxide in that mode.

Check the back or side of the alarm for a manufacture date or a "replace by" date. If it's past that date, or the chirping continues after a fresh battery, replace the alarm. Many alarms also show an "END" or "ERR" message on a display. Patterns differ by brand, so check the label on the alarm or the manual for yours.

Don't write off a false alarm

When an alarm goes off and the fire department finds no carbon monoxide, it's tempting to blame the alarm. Sometimes it really is a faulty or expired unit. But low levels of CO can come and go. A furnace that only spills exhaust during long run times on the coldest nights, a water heater that backdrafts when the bathroom fans and dryer are running, or a car started in the garage for a few minutes can all trigger an alarm that's gone by the time responders arrive.

If an alarm goes off more than once, or goes off and no clear cause is found, have your fuel-burning equipment inspected. Replace the alarm too if it's near its replacement date. It's far better to find a venting problem on a service call than to learn about it from a second alarm at 3 a.m.

Other sounds and codes

• A chirp right after you install a new battery can mean the battery isn't seated fully or the battery door isn't closed.
• Several chirps in a row, or an error message on the display, can mean the alarm has a fault. Most manuals list error codes on the back label.
• On combination smoke and CO alarms, the smoke alarm uses a different pattern, often three long beeps. Check the label so you know which is which.
• Interconnected alarms may all sound together when one detects a problem. The one that started it often has a flashing light.

Where carbon monoxide comes from in a Minnesota home

CO is produced whenever fuel burns. In Twin Cities homes, the usual sources are a gas furnace, boiler or water heater that isn't venting properly, a gas range or oven, a fireplace, a car warming up in an attached garage, or a generator running too close to the house.

Winter adds a few specific risks. Snow and ice can block the plastic vent pipes on high-efficiency furnaces and water heaters. Older water heaters left venting alone into an oversized chimney after a furnace upgrade can backdraft. And a cracked heat exchanger in an aging furnace can let combustion gases into the airstream. Our post on what a cracked heat exchanger means explains that one. Never warm up a car in an attached garage, even with the big door open.

Where your alarms should be

Minnesota law requires working CO alarms within 10 feet of every sleeping room. It's also smart to have one on each level of the house, including the basement near fuel-burning equipment, following the manufacturer's placement instructions. Our post on carbon monoxide and Minnesota's CO alarm law covers the requirements and testing.

Test your alarms monthly with the test button, replace batteries as the manufacturer recommends, and write the install date on each new alarm so you know when it's due for replacement.

Have your fuel-burning equipment checked

An annual furnace tune-up includes a check of the heat exchanger, venting and combustion, and it's the best way to catch a CO problem before an alarm ever has to. If your CO alarm went off and emergency responders have cleared the house, or you'd like your furnace, boiler or water heater checked for safe venting, call Heating & Cooling Two at 763-428-3677 or schedule a furnace repair. After-hours emergency service is available.