What does the chirp mean?
Smoke and CO alarm chirp patterns by brand, from the makers' own manuals and support pages (checked 2026-10-02).
A chirp is not an alarm. A chirp is one short beep (or a short group) every 30–60 seconds. If an alarm is sounding continuously, with three long beeps repeating (fire) or four short beeps repeating (carbon monoxide), get everyone out and call 911.
The short version
- 1 chirp every 30–60 seconds usually means a low battery. On a sealed 10-year alarm, where the battery can't be changed, it means the alarm needs replacing.
- 2 chirps often mean end of life (Kidde CO and combo alarms, X-Sense combos, USI 10-year alarms, Nest Protect). On some X-Sense alarms, 2 chirps every 40 seconds mean a fault.
- 3 chirps a minute usually mean a fault (First Alert, Kidde, USI), but end of life on some X-Sense and USI CO alarms and on older First Alert CO alarms.
- 5 chirps a minute on First Alert alarms mean end of life. On their sealed 10-year models it's the same signal for a spent battery: replace the alarm.
- Still chirping after a new battery? Check the date on the back label. Smoke alarms are replaced 10 years after the date of manufacture.
Patterns vary by model, even within one brand. On a Kidde smoke alarm, one chirp every 30–40 seconds is a low battery, one every 30 seconds on a sealed model is end of life, and a chirp between flashes of the red light is a fault. The tables below show the light that goes with each pattern where the maker gives one. When in doubt, the model number and date on the back label settle it, and your manual has the final word.
Kidde First Alert / BRK X-Sense Universal Security Instruments Google Nest Protect
Kidde
| Pattern | Type | Models | Means | Source |
|---|---|---|---|---|
| 1 chirp | Smoke | all | Fault (malfunction) Light: chirp falls between flashes of the red LED | manual |
| 1 chirp | Any | RGCUDR, RGSDR | Low battery | manual |
| 1 chirp every 30–40 s | Smoke | all | Low battery | manual |
| 1 chirp every 30–40 s | Smoke | smoke alarms with Hush | Hush / silence mode (temporary) | manual |
| 1 chirp every 30 s | Smoke | sealed-battery smoke models | End of life: replace the alarm | manual |
| 1 chirp every 30 s | CO | CO alarms | End of life: replace the alarm | manual |
| 1 chirp every 30 s | CO | CO alarms | Fault (malfunction) | manual |
| 1 chirp every 30 s | Smoke + CO | combination smoke/CO alarms | End of life or a sensor fault | manual |
| 1 chirp every 30 s | CO | non-digital CO alarms | End of life: replace the alarm Light: red LED flashes | manual |
| 1 chirp every 30 s | Smoke | 2070-VDSR | Fault (malfunction) Light: amber LED blinks every 30 s | manual |
| 1 chirp every 30 s | Smoke | 2070-VDSR | Fault (malfunction) | manual |
| 1 chirp every 40–45 s | Smoke | I9010, I9010CA | End of life: replace the alarm Light: red LED is the only LED | manual |
| 1 chirp every 40–45 s | Smoke | I9010CA | End of life: replace the alarm | manual |
| 1 chirp every minute | CO | CO alarms | Low battery | manual |
| 1 chirp every minute | Smoke + CO | combination smoke/CO alarms | Low battery | manual |
| 1 chirp every minute | Smoke | 2070-VDSR | Low battery Light: amber LED blink every 60 s | manual |
| 1 chirp every minute | Smoke | 20SDR-CA | Low battery Light: amber LED flash | manual |
| 1 chirp every minute | CO | COB10 | Low battery Light: amber LED blinks every 6 s | manual |
| 1 chirp every minute | CO | COBD10 | Low battery Light: amber LED blinks every 6 s | manual |
| 1 chirp every minute | CO | COBDL10 | Low battery Light: amber LED blinks every 6 s | manual |
| 2 chirps every 10 s | CO | COBDL10 | Low level of carbon monoxide Light: red LED blinks 2 times every 10 s | manual |
| 2 chirps every 30 s | CO | CO alarms | End of life: replace the alarm Light: digital models display "END" | manual |
| 2 chirps every 30 s | Smoke | 2070-VDSR | End of life: replace the alarm Light: amber LED blinks twice every 30 s | manual |
| 2 chirps every 30 s | CO | C3010-CA | End of life: replace the alarm | manual |
| 2 chirps every minute | Smoke + CO | 30CUD10-CA | End of life: replace the alarm Light: amber LED flashes | manual |
| 2 chirps every minute | CO | COB10 | End of life: replace the alarm Light: amber LED blinks twice every 60 s in sync with chirps | manual |
| 2 chirps every minute | CO | COBD10 | End of life: replace the alarm Light: amber LED blinks twice every 60 s in sync with chirps | manual |
| 2 chirps every minute | CO | COBDL10 | End of life: replace the alarm Light: amber LED blinks twice every 60 s in sync with chirps | manual |
| 2 chirps every minute | Smoke + CO | RGCUDR, RGCUDR-RW, RGSDR | End of life: replace the alarm Light: amber LED flashes | manual |
| 2 chirps every minute | Smoke | RGCUDR, RGSDR, RGSDR-RW | End of life: replace the alarm Light: amber LED flashes | manual |
| 3 chirps | Smoke | RGCUDR, RGSDR, RGSDR-RW | Needs cleaning Light: one blink (colour not stated; amber means fault on this model) | manual |
| 3 chirps every minute | CO | COB10 | Fault (malfunction) Light: amber LED blinks twice every 60 s | manual |
| 3 chirps every minute | CO | COBD10 | Fault (malfunction) Light: amber LED blinks twice every 60 s | manual |
| 3 chirps every minute | CO | COBDL10 | Fault (malfunction) Light: amber LED blinks twice every 60 s | manual |
| 3 chirps every minute | Smoke | RGCUDR, RGSDR | Needs cleaning Light: amber = fault / error | manual |
First Alert / BRK
| Pattern | Type | Models | Means | Source |
|---|---|---|---|---|
| 1 chirp every 45 s | Smoke + CO | SMCO500V | Low battery Light: power/smoke LED flashes green about every 45 s | manual |
| 1 chirp every minute | Smoke | smoke alarms | Hush / silence mode (temporary) | manual |
| 1 chirp every minute | Smoke | 9120B | Low battery Light: red LED flashes once per minute | manual |
| 1 chirp every minute | CO | CO400 | Low battery Light: red light keeps flashing | manual |
| 1 chirp every minute | Smoke + CO | SC5 | Low battery Light: halo LED: 1 amber flash every minute | manual |
| 1 chirp every minute | Smoke + CO | SC9120B | Low battery Light: green LED flashes with the horn | manual |
| 1 chirp every minute | Smoke + CO | SCO5CN | Low battery | manual |
| 1 chirp every minute | Smoke + CO | SMCO200 | Low battery Light: green power LED flashes about once a minute | manual |
| 1 chirp every minute | Smoke + CO | SMCO200V, SMICO100 | Low battery | manual |
| 1 chirp every minute | Smoke | SMI100 | Low battery Light: green power LED flashes 1 time every minute | manual |
| 3 chirps | Smoke | SA3210 | Fault (malfunction) | manual |
| 3 chirps every 45 s | Smoke + CO | SMCO500V | Fault (malfunction) Light: power/smoke LED flashes green in sync | manual |
| 3 chirps every minute | CO | CO400 | Fault (malfunction) Light: red light flashes | manual |
| 3 chirps every minute | CO | CO410 | Fault (malfunction) Light: red light flashes; display shows "ERROR" | manual |
| 3 chirps every minute | CO | CO5-B10D | Fault (malfunction) Light: display shows "Err" | manual |
| 3 chirps every minute | CO | CO600 | Fault (malfunction) Light: power/alarm light flashes three times in sync | manual |
| 3 chirps every minute | CO | CO600, CO410, SC9120B, CO5120BN | End of life: replace the alarm Light: power/alarm light flashes three times in sync | manual |
| 3 chirps every minute | CO | CO710 | Fault (malfunction) Light: display shows "Err" | manual |
| 3 chirps every minute | Smoke + CO | SC5 | Fault (malfunction) Light: halo LED: 2 amber flashes once a minute | manual |
| 3 chirps every minute | Smoke + CO | SC9120B | Fault (malfunction) Light: green LED flashes 3 times in sync | manual |
| 3 chirps every minute | Smoke + CO | SCO5CN | Fault (malfunction) Light: LED 3 rapid flashes with the chirps | manual |
| 3 chirps every minute | Smoke + CO | SMCO200 | Fault (malfunction) Light: three green flashes about once a minute | manual |
| 3 chirps every minute | Smoke + CO | SMCO200V, SM210, SM210V, SMCO210V, SMICO110 | Fault (malfunction) | manual |
| 3 chirps every minute | Smoke | SMI100 | Fault (malfunction) Light: green power LED flashes 3 times every minute | manual |
| 5 chirps every 45 s | Smoke | SA3210 | Sealed battery spent: replace the alarm | manual |
| 5 chirps every 45 s | Smoke + CO | SMCO500V | End of life: replace the alarm Light: power/smoke LED flashes green in sync | manual |
| 5 chirps every minute | CO | CO400 | End of life: replace the alarm Light: red light flashes | manual |
| 5 chirps every minute | CO | CO5-B10D | End of life: replace the alarm Light: display shows "End" | manual |
| 5 chirps every minute | CO | CO710 | End of life: replace the alarm Light: display shows "End" | manual |
| 5 chirps every minute | Smoke + CO | SC5 | End of life: replace the alarm Light: power LED 5 flashes; halo LED 1 amber flash | manual |
| 5 chirps every minute | Any | SM210, SM210V, SMCO210V, SMICO110 | Sealed battery spent: replace the alarm | manual |
| 5 chirps every minute | Smoke + CO | SMCO200 | End of life: replace the alarm Light: five green flashes about once a minute | manual |
| 5 chirps every minute | Smoke + CO | SMCO200V, SMICO100 | End of life: replace the alarm | manual |
| 5 chirps every minute | Smoke | SMI100 | End of life: replace the alarm Light: green power LED flashes 5 times every minute | manual |
X-Sense
| Pattern | Type | Models | Means | Source |
|---|---|---|---|---|
| 1 chirp every minute | Smoke + CO | SC01, SC02, SC07, SC08 | Low battery Light: flashes yellow once every 60 seconds | manual |
| 1 chirp every minute | Smoke | SD19-W, SD20-W | Low battery Light: red LED flashes once every 60 seconds | manual |
| 1 chirp every minute | CO | XC01, XC04 | Low battery Light: flashes yellow once every 60 seconds | manual |
| 1 chirp every minute | CO | XC04-WX | Low battery Light: flashes yellow every 60 seconds | manual |
| 1 chirp every minute | Smoke | XS01, XS0301 | Low battery Light: red LED flashes every 60 seconds | manual |
| 2 chirps every 30 s | Smoke + CO | SC01, SC02, SC07, SC08 | End of life: replace the alarm Light: flashes yellow twice every 30 seconds | manual |
| 2 chirps every 40 s | Smoke + CO | SC01, SC02, SC07, SC08 | Fault (malfunction) Light: yellow 1-2 flashes per 40 s = smoke fault; 3-4 flashes per 40 s = CO fault | manual |
| 2 chirps every 40 s | Smoke | SD19-W, SD20-W | Fault (malfunction) Light: red LED flashes twice every 40 seconds | manual |
| 2 chirps every 40 s | Smoke | XS01, XS0301 | Fault (malfunction) Light: red LED flashes twice every 40 seconds | manual |
| 2 chirps every minute | CO | XC01, XC04, XC01-R, XC04-R | Fault (malfunction) Light: flashes yellow 2 times every 60 seconds | manual |
| 3 chirps every minute | CO | XC01, XC04, XC01-R, XC04-R | End of life: replace the alarm Light: flashes yellow 3 times every 60 seconds | manual |
| 3 chirps every minute | CO | XC04-WX | End of life: replace the alarm Light: flashes yellow 3 times every 60 seconds | manual |
Universal Security Instruments
| Pattern | Type | Models | Means | Source |
|---|---|---|---|---|
| 1 chirp every 40 s | CO | USI/CO/REP | Low battery Light: yellow FAULT indicator flashes | manual |
| 1 chirp every minute | Smoke | USI/SM/10YR, USI/SM/10YR/3 | Low battery Light: red LED blinks once about every 2 minutes | manual |
| 1 chirp every minute | Smoke + CO | USI/SMCO/10YR | Low battery Light: 1 blink about every 2 minutes | manual |
| 2 chirps every 40 s | CO | USI/CO/REP | Fault (malfunction) Light: yellow FAULT indicator flashes; LCD "Err" | manual |
| 2 chirps every minute | CO | MC304S, MCD305S | End of life: replace the alarm Light: LED off | manual |
| 2 chirps every minute | Smoke | USI/SM/10YR | Low battery Light: red LED blinks once about every 2 minutes | manual |
| 2 chirps every minute | Smoke | USI/SM/10YR, USI/SM/10YR/3 | End of life: replace the alarm Light: red LED blinks once about every 2 minutes | manual |
| 2 chirps every minute | Smoke + CO | USI/SMCO/10YR | End of life: replace the alarm Light: 1 blink about every 2 minutes; CO LED off | manual |
| 3 chirps every 40 s | CO | USI/CO/REP | End of life: replace the alarm Light: yellow indicator flashes three times; LCD "End" | manual |
| 3 chirps every minute | CO | MC304S, MCD305S | Fault (malfunction) Light: red LED blinks about every 2 seconds | manual |
| 3 chirps every minute | Smoke + CO | USI/SMCO/10YR | Fault (malfunction) Light: red smoke LED blinks once about every 2 minutes; CO LED off | manual |
Google Nest Protect
| Pattern | Type | Models | Means | Source |
|---|---|---|---|---|
| 1 chirp every minute | Smoke + CO | Nest Protect | Low battery Light: pulsing yellow light ring | manual |
| 1 chirp every minute | Smoke + CO | Nest Protect | Fault (malfunction) Light: pulsing yellow light ring | manual |
| 2 chirps every minute | Smoke + CO | Nest Protect | End of life: replace the alarm Light: pulsing yellow light ring | manual |
Find which alarm it is
A high, short chirp once a minute is hard to place by ear. It reflects off ceilings and walls. Chirp Finder counts down to the next chirp, measures it under each alarm and ranks them, then decodes the pattern for that alarm's model and reads the date off its label. Coming soon to the App Store