Carbon Monoxide Detector Beeping: What Each Pattern Means
If the alarm is sounding a loud, repeating pattern right now, treat it as real. Get everyone outside into fresh air, then call your emergency services or gas utility from outside the building. Do not open windows to "clear it" first and do not go back in to investigate. Carbon monoxide has no smell, so the alarm is the only warning you get, and a false alarm costs you an evening while a real one costs more than that.
There are two completely different noises a carbon monoxide alarm makes, and almost every question about beeping comes down to telling them apart.
The alarm, and the chirp
A loud repeating pattern that does not stop is the alarm signal. The unit believes it is detecting carbon monoxide. This is the sound described above: leave, then call from outside.
A single short chirp every 30 to 60 seconds is maintenance, not detection. The unit is telling you something about itself: usually that its battery is low, or that it has reached the end of its service life. It is deliberately annoying because a dead alarm protects nobody, and because people who could not hear it would ignore it.
The exact number of beeps in each pattern is set by the manufacturer, and it is printed in the user guide for your specific model rather than shared across brands. Find the model number on the back of the unit before you go looking: a "Kidde beeping" search will hand you an answer meant for a different product in the same range.
First Alert: one, three or five chirps
First Alert publishes its chirp patterns on its support site, which makes it the one brand where the count can be read straight off a table. Each pattern repeats about once a minute.
| Chirps | What First Alert says it means | What First Alert says to do |
|---|---|---|
| 1 | Low battery. Also a battery in backwards, a drawer left partly open, or a pull-tab still in place | Fit a fresh battery and close the drawer fully. Units on 9V or AA cells need new batteries at least once a year |
| 3 | Malfunction warning | Cut power at the breaker for a minute, clean the unit and run a test. If it continues, the unit is faulty |
| 5 | End of life. On a brand new unit, a backup battery that is not activated | Replace an alarm that is over 7 years old. The test button quiets the warning for about 2 days at a time, and after roughly 2 to 3 weeks it can no longer be silenced |
Source: First Alert support, what the chirps mean, read 1 October 2026.
Two details in that table are easy to miss. Unplugging the alarm or pulling the battery does not stop a low-battery chirp. And five chirps on an alarm that came out of the box last week is usually the battery backup, not a dead sensor: First Alert says to check that the unit is twisted fully onto its bracket.
This table is First Alert's. Kidde and other makers use their own counts, so a Kidde unit chirping five times is not covered by it: go by the guide for that model.
A chirp that a new battery does not fix
Carbon monoxide alarms expire. The electrochemical sensor inside them degrades whether or not it has ever seen carbon monoxide, which is why manufacturers give the unit a service life and build in an end-of-life signal to announce it. That signal is frequently mistaken for a battery fault, and a new battery quiets it for a few seconds before it resumes.
Two things to check on the unit itself:
- The date on the back. Manufacturers print a manufacture date, and some print a replace-by date directly. The service life runs from manufacture, not from the day you opened the box or plugged it in.
- Whether the chirp survives a fresh battery. If it does, the unit is finished. No amount of resetting brings a spent sensor back, and a unit that has announced end of life should be replaced rather than silenced.
How long alarms last covers the dates on the back of the unit and why the test button cannot tell you a sensor is still alive. If you are at that point, our carbon monoxide alarm collection covers the two designs worth choosing between: a battery-only alarm that keeps working through a power cut by design, and a plug-in alarm with a digital display that shows the current reading in parts per million.
Why a display changes what you can do
An alarm without a display has exactly two states: quiet, and sounding. It tells you nothing about a low-level exposure that has not reached the alarm threshold, and nothing about whether a reading has been climbing all week.
A unit with a parts-per-million display is the one that lets you answer the next question, because you can see whether a number is zero, steady, or rising after the boiler runs. That is also why a display is worth more in a house with older fuel-burning appliances than in an all-electric flat.
What not to do
- Do not silence and forget. The silence button suppresses the sound for a fixed period; it does not decide whether the cause was real.
- Do not remove the battery to stop the noise. This is the most common way an alarm ends up permanently out of service, and it always happens at night.
- Do not move the alarm to a quieter spot because it chirps there. Mounting position follows the manufacturer's instruction for the model, and a unit mounted where nobody hears it is decoration: where to place one covers the rooms that matter.
- Do not treat a CO alarm as a gas leak detector. They answer different questions, and only some products do both. Our gas leak detector collection covers the combination units and the difference.
When the alarm sounds and nobody feels unwell
That happens, and it does not mean the alarm is faulty. Carbon monoxide affects people at different rates depending on age, health and how long they have been in the room, and an alarm is calibrated to sound before most people notice anything. Symptoms are also easy to mistake for something ordinary: headache, dizziness, nausea, unusual tiredness. Leave first, then let the people with instruments decide whether the reading was real. This page is not medical advice; if anyone feels unwell, say so when you call.