Smoke or CO alarm beeping: decode the pattern before you touch it

Clocks go back this weekend, and the furnace is about to run for the first time in months. For a lot of homes, that is also the week an alarm starts to chirp in the middle of the night. It is tempting to pull the battery, silence the thing and go back to sleep. Before you do, spend a minute working out what the sound is saying.

An alarm can make noise for very different reasons: the battery is low, the unit is worn out, or something is actually wrong in the house. The first two are routine household jobs. The last is an emergency, and carbon monoxide (CO) gives you no help of its own: the EPA says it cannot be seen, tasted or smelled, and CPSC calls it colorless, odorless and poisonous.

So start by identifying which kind of alarm is sounding: smoke, CO or a combination unit. If you are not sure, treat it as a CO alarm and treat it as an emergency. This guide gives you a pattern-to-meaning decoder, the steps a homeowner can safely take, and the point where you stop and call a licensed electrician.

What's going on

Alarm makers use beep patterns as a language, and the code differs by brand and model. Your printed manual or the maker's support page always wins over any table, including this one. Before you read the table, do two things: find out whether the alarm is a smoke alarm, a CO alarm or a combination unit, and remember that if you cannot tell, you treat it as a CO emergency.

The table below pulls together what two alarm makers publish on their own pages. Use it as a first read, not a final answer.

| What you hear | Alarm type | Usual meaning | What the maker says to do |
|---|---|---|---|
| Four beeps, then a pause | CO | CO detected: an emergency | Move to fresh air and call 911 |
| One beep or chirp every minute | CO | Low battery | Replace the battery |
| Five beeps every minute | CO | End of life | Replace the alarm |
| A chirp every 30 seconds | CO | End of life (seven years after power-up on one maker's units) or an error such as very low battery or malfunction | Do not rely on it; follow the manual or replace it |
| A chirp every 30 to 40 seconds (60 on some models) for at least seven days | Smoke | Low battery | Replace the battery |
| A chirp every 30 to 40 seconds for about seven minutes | Smoke | Hush mode running | Nothing; it runs for that time |
| A chirp every 30 seconds on a sealed-battery unit | Smoke | End of life | Replace the alarm |
| A chirp between red light flashes | Smoke | Possible malfunction | Hold the Test button for two seconds to check |

The same chirp can mean different things on a smoke alarm and a CO alarm, which is why identifying the type comes first. On a combination unit the manual is the only reliable key.

An end-of-life CO alarm is not just annoying. One maker warns that an alarm in that state will not respond to carbon monoxide. Another maker advises replacing CO alarms after seven years even if the battery is good, because the sensor degrades.

Temperature can also matter. One maker says its smoke and CO alarms perform between 40 and 100 degrees Fahrenheit, so an alarm in a garage, attic or unheated space may behave oddly. Check your manual for the right placement.

Sources: a CO alarm guide from a manufacturer and another maker's chirping-causes page.

What you can safely check or fix

These steps are for a plug-in or battery-powered alarm that you can reach from the floor or a stable stool. If your alarm is wired into the house, read the stop line in the next section first. Steps 1 to 3 come first because they are the safety steps. If none of that applies, go on to step 4.

1. If a CO alarm is sounding four beeps and a pause, or anyone feels sick, leave the house and get to fresh air.
2. Call 911 once you are outside.
3. Keep others out of the house until the fire department says it is clear.
4. Stand near the alarm and listen to the gap between beeps.
5. Read the label to see whether it is a smoke, CO or combination alarm.
6. Find your model's manual or the maker's support page.
7. Match the pattern you heard to the chart in that manual.
8. If a smoke alarm chirps between red light flashes, hold the Test button for two seconds.
9. If the pattern says low battery, replace the battery with the type the manual names.
10. Press the Test button and listen for the normal alarm tone.
11. Follow only the cleaning or reset steps your manual lists for your model.
12. If the pattern says end of life, or a CO alarm is past seven years old, replace the whole alarm.
13. Check the new alarm's box for a listing to UL 2034 or IAS 6-96 if it is a CO alarm.

A few notes on those steps. A hushed smoke alarm chirps for about seven minutes and then stops by itself, so a short burst of chirping after you silenced it is not a new problem. A low-battery smoke chirp can run for at least seven days, so do not wait it out. A new battery will not fix a worn-out sensor. For the monthly test habit, see the routine at the end.

Where to stop and call a pro

Some beeping points outside the alarm. If the alarm is wired into the house, or a CO alarm has sounded in a home with fuel-burning appliances, the fix is no longer a household battery swap.

Stop here: If your alarm is hardwired to the house wiring, call a licensed electrician. Do not open ceiling boxes or touch the wiring yourself. Wiring and circuits are licensed work, and this guide gives no steps for them.

The second half of the line is a short pointer. If a CO alarm sounded and your home has a furnace, water heater, gas stove or fireplace, get everyone out, call 911 and stay out until the fire department clears the home. Then have a qualified heating professional look at the appliances rather than restarting them yourself.

The source of CO is usually an appliance. The EPA lists unvented heaters, leaking chimneys and furnaces, and gas stoves among the sources. CPSC urges an annual professional inspection of fuel-burning appliances to find leaks, and the EPA recommends an annual inspection and tune-up of central heating systems. Early symptoms can look like the flu, so do not talk yourself out of it because it seems minor.

Outdoors, CPSC also advises clearing snow from the vents of fuel-burning appliances such as furnaces. If you do that, only move the snow. Leave the vent hardware and the appliance alone.

Sources: CPSC winter safety tips, CPSC on annual inspections, and the EPA on CO and indoor air.

What to tell the pro

A short, specific report saves a visit. Have these ready before you call:

• The exact beep pattern and how often it repeats, with a phone recording if you can make one.
• Whether it is a smoke alarm, CO alarm or combination unit, and whether it is wired or battery-powered.
• Roughly how old the alarm is, and whether the battery was recently changed.
• Whether it started after you ran the furnace, a space heater, a gas stove or a generator for the first time this season.
• Whether anyone had headaches, dizziness, nausea or flu-like symptoms, and whether they eased once outside.
• Whether the fire department responded and what they told you.
• Which fuel-burning appliances you have, and when each was last inspected.

Early CO symptoms can pass for the flu, and an annual inspection of heating equipment is the usual advice, so a pro will want that history.

A heating-season routine

The weekend the clocks change is a handy reminder, not a rule. CPSC says to test alarms monthly, so put a recurring monthly reminder on your phone calendar once the new alarm is up. It also advises smoke alarms on every level and inside each bedroom, and CO alarms on every level and outside sleeping areas. It recommends interconnected CO alarms, so that all of them sound when one does.

If you run a generator during an outage, the CDC advises keeping it at least 20 feet from doors, windows and vents. The CDC and NIOSH also recommend a battery-operated CO detector so the alarm still works when power fails.

CO is serious: CPSC counts over 200 US deaths a year from non-fire CO tied to consumer products. A chirp you handle on a Saturday is cheap compared to that.

Quick answers

Is a chirping alarm a low battery or an emergency?

A single chirp every minute or so is usually a low battery, but four beeps and a pause on a CO alarm means CO was detected. If you are not sure what kind of alarm it is, treat it as a CO emergency: get outside and call 911.

How do I know if my CO alarm is expired?

Five beeps every minute, or a chirp every 30 seconds on some models, signals end of life. Replace CO alarms after 7 years, because an expired one may not detect CO.

Can I fix a hardwired alarm that keeps beeping?

Stop at the wiring and call a licensed electrician. If a CO alarm sounded near fuel-burning appliances, get out, call 911 and have the appliances inspected.