What battery does a carbon monoxide detector take?
In these models, a CO alarm takes 2 AA batteries, one 9V, a CR123A, 2 AAA as a plug-in backup or a sealed battery you never change.
Which alarm?
The battery it takes
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CO alarm batteries by model
Carbon monoxide alarm batteries by maker and model
Alarm
Power
Battery
Kidde COB, COBD, COBDL
Battery
2 AA alkaline
Kidde COB10, COBD10, COBDL10
Sealed
None to change
Kidde COP, COPD, COPDLG
Plug-in
2 AA backup
Kidde COPDL10
Plug-in
Sealed 10-year backup
First Alert CO400
Battery
One 9V
First Alert CO410
Battery
2 AA
First Alert CO710
Sealed
None to change
First Alert CO606
Plug-in
One 9V backup
X-Sense XC0C-SR
Battery
2 AA
X-Sense XC01-R, XC0M-SR
Battery
One CR123A
X-Sense XC0C-SA
Plug-in
2 AAA backup
From each maker’s manual or product page. Combined smoke and CO alarms are on the smoke detector page.
What the chirps mean
Low battery and end of life signals, from each maker
Alarm
Low battery
Replace the alarm
Kidde battery and plug-in models
A chirp every 60 seconds
2 chirps every 60 seconds
First Alert CO606
One chirp a minute
5 chirps every minute
First Alert CO400, CO710
Not listed
5 chirps every minute
First Alert CO410
Not listed
Not listed
X-Sense XC0C-SR
Lb on the screen
End on the screen
From Kidde’s and First Alert’s manuals and X-Sense’s product pages.
Don’t mix batteries
Kidde’s guides say not to mix old and new batteries in its CO alarms, or alkaline, standard and rechargeable ones. Use only the batteries the guide names.
Keep the plug-in alarm working
First Alert’s CO606 manual says not to unplug the alarm or take its battery out until you have a replacement ready.
Common questions
Why won't the battery door close on my Kidde CO alarm?
Kidde says the battery door on its COB, COBD and COBDL alarms won't close if either AA battery is missing.
Can I silence the end of life chirp on a First Alert CO alarm?
First Alert says the CO400's end of life signal can be silenced for up to 2 days, but the alarm still has to be replaced.
From Kidde’s and First Alert’s user manuals and X-Sense’s product pages, read on October 25, 2026. Checked against published data from First Alert, Kidde and X-Sense.
See all 7 sources
Kidde, Battery Powered Carbon Monoxide Alarms user guide (G-000069-00: COB, COBD, COBDL, COB10, COBD10, COBDL10), PDF
Kidde, AC Plug-In Carbon Monoxide Alarms user guide (G-000068-00: COP, COPD, COPDL10, COPDLG), PDF
First Alert, CO400 Battery-Operated Carbon Monoxide Alarm (product page and user's manual M08-0140-029)
First Alert, CO606 Plug-In Carbon Monoxide Alarm with Battery Backup (product page and user's manual M08-0206-008)
First Alert, CO710 10-Year Battery Carbon Monoxide Alarm (product page and user's manual)
First Alert, CO410 Battery Operated Carbon Monoxide Alarm with Backlit Digital Display (product page)
Battery sizes come from battery makers' datasheets and device makers' own manuals and help pages. Check your device's manual or the old battery before you buy. If anyone may have swallowed a battery, call the National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222 straight away.