First Alert CO alarm: 5 chirps every minute means end of life
Five chirps every minute is First Alert’s end of life signal on its CO and combination alarms: the alarm has reached the end of its service life and has to be replaced; new batteries will not stop it. It arrives about 7 years after installation on the CO400 and SCO5 and about 10 years on the sealed SMCO210 and CO710. Silencing it buys about 2 days.
If it is sounding a full alarm: First Alert’s carbon monoxide instruction
Carbon monoxide alarm
First Alert (SCO5, SMCO210 and CO710 manuals): “If you hear the CO alarm horn and the CO red light is flashing, move everyone to a source of fresh air.” Then: press the Test/Silence button; “call your emergency services, fire department or 911”; “immediately move to fresh air—outdoors or by an open door or window” and do a head count. Do not go back in until the emergency services responder has arrived, the premises have been aired out and the alarm is back to normal. If it sounds again within 24 hours, repeat those steps and call a qualified appliance technician.
From Model SCO5 manual, Model SMCO210 manual, Model CO710 manual.
End of life, model by model
4 First Alert models whose manuals we read. The model number is on the label on the back of the alarm. If yours is not here, its own manual is the authority: First Alert models do not all use the same lights.
| Model | What you see | What you hear |
|---|---|---|
| CO400 battery CO alarm, one 9-volt battery | Red light flashing | 5 chirps every minute |
| SCO5 combination smoke and CO alarm, two AA batteries | Green light flashing | 5 chirps every minute |
| SMCO210 combination smoke and CO alarm, 10-year sealed battery | Five green flashes about once a minute | 5 chirps every minute |
| CO710 CO alarm with digital display, 10-year sealed battery | Display shows “End” | 5 chirps every minute |
First Alert CO400: battery CO alarm, one 9-volt battery
- What you see
- Red light flashing
- What you hear
- 5 chirps every minute
“The light flashes (RED) and the horn sounds 5 ‘chirps’ every minute. END OF LIFE SIGNAL. CO Alarm needs to be replaced. Immediately replace the CO Alarm.”
What the CO400 manual says to do
- Replace the CO alarm. The manual asks you to “Replace alarm 5 years after installation” and adds that the end of life signal comes “approximately 7 years after installation”.
- The Test/Silence button quiets it “for up to 2 days”; after that the chirp resumes.
Source:
- First Alert (BRK Brands): Battery Operated Carbon Monoxide Alarm with Silence Feature — User’s Manual — Model CO400 (manual M08-0140-029). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
First Alert SCO5: combination smoke and CO alarm, two AA batteries
- What you see
- Green light flashing
- What you hear
- 5 chirps every minute
“The light flashes GREEN and the horn sounds 5 ‘chirps’ every minute. END OF LIFE SIGNAL. Alarm needs to be replaced. Immediately replace the Alarm.”
What the SCO5 manual says to do
- Replace the alarm: the end of life signal comes “approximately 7 years after installation”. Fresh AA batteries do not clear it.
- Pressing Test/Silence quiets it for up to 2 days; “The horn will chirp, acknowledging that the End of Life silence feature has been activated.”
Source:
- First Alert (BRK Brands): Combination Carbon Monoxide & Smoke Alarm — User’s Manual — Model SCO5 (manual M08-152696-SCO5-US). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
First Alert SMCO210: combination smoke and CO alarm, 10-year sealed battery
- What you see
- Five green flashes about once a minute
- What you hear
- 5 chirps every minute
“Alarm has reached its End of Life — Horn: 5 chirps every minute; Power LED: Five Green flashes approximately once a minute.”
What the SMCO210 manual says to do
- Replace the alarm: First Alert says “Replace Alarm 10 years after installation”, and the signal comes “approximately 10 years after installation”.
- Then deactivate the old one (break the tab and slide the switch to deactivate) so the sealed battery’s stored energy is drained.
- One green flash with 5 chirps is this model’s low battery signal; it also means replace the alarm.
Source:
- First Alert (Resideo): Smoke & Carbon Monoxide Alarm, 10-Year Sealed Battery — User’s Manual — Model SMCO210 (manual M08-0600-000). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
First Alert CO710: CO alarm with digital display, 10-year sealed battery
- What you see
- Display shows “End”
- What you hear
- 5 chirps every minute
“CO Alarm End of Life: The horn sounds 5 chirps every minute. CO alarm needs to be replaced. ‘End’ is displayed.”
What the CO710 manual says to do
- Install a new CO alarm: the battery is sealed and “Once it reaches the end of its service life, or after 10 years—whichever comes first—you must install a new CO alarm.”
- Deactivate the old one with the tab and switch on the back; “Once you deactivate this unit, it will not detect CO or alarm and cannot be reactivated.”
Source:
- First Alert (BRK Brands): Carbon Monoxide Alarm, 10-Year Sealed Battery, with Digital Temperature Display — User’s Manual — Model CO710 (manual M08-0534-160326-US Rev B). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
Not the signal you have?
Sources
Every line on this page comes from First Alert’s own user’s manuals, read on the date shown; the quotes are the manuals’ words. firstalert.com’s product pages link these manuals as their downloads; the files are kept on the asset host of Resideo, which owns First Alert.
- First Alert (BRK Brands): Battery Operated Carbon Monoxide Alarm with Silence Feature — User’s Manual — Model CO400 (manual M08-0140-029). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
- First Alert (BRK Brands): Combination Carbon Monoxide & Smoke Alarm — User’s Manual — Model SCO5 (manual M08-152696-SCO5-US). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
- First Alert (Resideo): Smoke & Carbon Monoxide Alarm, 10-Year Sealed Battery — User’s Manual — Model SMCO210 (manual M08-0600-000). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
- First Alert (BRK Brands): Carbon Monoxide Alarm, 10-Year Sealed Battery, with Digital Temperature Display — User’s Manual — Model CO710 (manual M08-0534-160326-US Rev B). digitalassets.resideo.com Checked 2026-10-13. Linked as the manual from First Alert’s product page www.firstalert.com Checked 2026-10-13.
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