Smoke and CO Alarm Beep Decoder
Pick your alarm type and the sound it makes to see what it means and what to do: emergency patterns, low battery, malfunction and end of life, using Kidde and First Alert guidance.
Decoder
Low battery
A single chirp about once a minute is the low-battery signal on Kidde and First Alert alarms.
Replace the battery with the type printed on the alarm, and close the battery door fully.
Press and hold the Test button to check the horn.
A sealed 10-year alarm cannot take a new battery: if one of those chirps, replace the whole alarm.
How the decoder works
Each answer comes from the makers’ own support pages and manuals, listed under Sources. The two emergency patterns are the same across brands: three beeps and a pause means smoke, and four beeps and a pause means carbon monoxide. The maintenance chirps differ by brand and model, so the decoder asks for the brand and says so when a pattern is not in our sources.
If in doubt, treat it as real. A loud, repeating alarm is never a battery problem. Get everyone out and call 911 from outside. Never remove the battery or disconnect an alarm to stop the noise and leave it that way.
Beep patterns at a glance
| What you hear | Meaning | Source |
|---|---|---|
| Three loud beeps, pause, repeating | Smoke detected: get out, call 911 | First Alert |
| Four loud beeps, pause, repeating | Carbon monoxide detected: get out, call 911 | Kidde, First Alert |
| One chirp every 30 to 60 seconds | Low battery | Kidde, First Alert |
| One chirp every 30 seconds, new battery fitted | End of life or malfunction: replace | Kidde |
| Three chirps every minute | Malfunction: replace (smoke alarms) | First Alert manuals |
| Five chirps every minute | End of life: replace | First Alert |
| One long, continuous tone (CO alarm) | Unplugged or loose, or a malfunction | Kidde |
Frequently asked questions
What does it mean when a smoke detector beeps three times?
Three loud beeps, a pause, then three more is the smoke alarm pattern. First Alert calls it an emergency: get everyone out and call 911 once you are outside.
What does four beeps on a carbon monoxide detector mean?
Four short beeps followed by a pause means the alarm may have detected carbon monoxide. Move everyone to fresh air and call 911. Kidde and First Alert use the same pattern.
Why does my alarm keep chirping after I changed the battery?
On many alarms a chirp that a new battery does not stop is the end-of-life signal. Kidde CO alarms chirp every 30 seconds at end of life; First Alert alarms give five chirps every minute. Either way, replace the alarm.
How often should I test my smoke alarms?
The U.S. Fire Administration says to test every smoke alarm monthly with its Test button, replace 9-volt and backup batteries at least once a year, and replace alarms every 10 years, or as the maker instructs for sealed long-life models.
Sources and method
- What Causes Consistent Chirping? Kidde
- Why Is My Carbon Monoxide Alarm Beeping or Chirping? Kidde
- How to Tell If Your Smoke Alarm is Working Kidde
- Why Is My Carbon Monoxide Detector Beeping? First Alert
- Why Is My Smoke Detector Beeping? First Alert
- User’s Manual: Smoke Alarm, AC Powered, Dual Sensor With Battery Backup, Model SM300-AC First Alert
- User’s Manual: Smoke Alarm, 10-Year Sealed Battery With Voice & Location, Model SM210V First Alert
- Smoke Alarms U.S. Fire Administration (FEMA)
Last reviewed . It explains common signals and does not replace the manual for your model or a qualified professional.