On this page
A chirp from the hallway at night means the carbon monoxide detector battery is spent, so here is how to replace carbon monoxide detector battery: open the cover, swap the spent battery for a fresh battery of the same size, close the cover, and press the button on the face of the unit to hear the beep. The steps below walk through each move, what to check before you start, and when the unit itself needs replacing instead.
SolarKitHQ earns a commission when you buy through links on this page, at no extra cost to you. As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure.
How to replace carbon monoxide detector battery: the quick answer
Twist or slide the detector off its base, open the battery cover, and lift out the spent battery. Match the plus and minus marks in the compartment, press a fresh battery of the same size into place, and close the cover. Put the detector back on its base and press the button on the face of the unit: a beep means the new battery is in place and the unit is live. If the unit chirps again right away, check the battery seating and the size on the label.
Step 1: Find the battery the unit takes
Read the label on the back of the detector or inside the battery cover: it names the battery size and type the unit takes. Buy the same size, since a battery that does not fit the compartment will not sit flat against the contacts. Keep a spare battery with the detector manual so the next chirp does not catch you without a spare. If the label is worn, the model number on the unit lets the maker identify the battery it takes.
Step 2: Take the detector off its base
Most detectors twist off a wall or ceiling base, while others slide off a bracket or pull straight down. Hold the detector with a hand under it so it does not fall, and turn or slide it gently until it comes free. Set it on a table with the face down and the back toward you. Hardwired detectors with a backup battery usually have a battery door too, so the battery can be swapped as in the steps below. Do not pull on the wires: only call a licensed electrician if the unit must be unwired or replaced.
Step 3: Swap the battery
Open the battery cover with a thumb on the latch or the tab, and lift the spent battery out. Note which way the plus and minus ends sit before you lift it out, since the new battery must sit the same way. Press the fresh battery into the compartment so the ends meet the contacts, and close the cover until it clicks. A battery that sits loosely will chirp again, so press it flat and check the cover is shut.
| Part | What to check |
|---|---|
| Battery | Same size as the label, ends matched to the marks, pressed flat |
| Cover | Shut until it clicks |
| Base | Seated on the bracket, locked in place |
| Button | Press and listen for the beep |
Step 4: Put the detector back and check it
Set the detector back on its base and twist or slide it until it seats. Press the button on the face of the unit and listen for the beep, which tells you the new battery is live and the alarm can sound. If the unit stays silent, open the cover again and check the battery seating and the plus and minus ends. If the unit chirps again right away with a fresh battery seated well, read the next section, because the unit itself may be at the end of its life.
Sealed units and end-of-life chirps
Some detectors are sealed long-life units with no replaceable battery. If you cannot find a battery door, check the label or the manual to see which type you own. An end-of-life chirp differs from a low-battery chirp: the pattern is not the same, and the manual describes both. Follow the maker’s replacement date printed on the unit, and replace the whole detector when that date arrives instead of hunting for a battery.
Ways to keep the detector ready
- Keep a spare battery: store the size the label names with the detector manual, so a night chirp does not wait for a shop trip.
- Note the date: write the date on the battery or the cover when you fit it, so you know how old the battery is when the next chirp comes.
- Keep the vents clear: dust the vents with a soft dry cloth so air reaches the sensor.
- Keep fuel generators outdoors: fuel generators run outdoors only, far from doors and windows, because of carbon monoxide.
- Replace the unit when it fails: if a fresh battery seated well does not stop the chirp, or the unit stays silent when you press the button, replace the unit rather than the battery.
FAQ: power away from the grid
Why does my carbon monoxide detector keep chirping?
A chirp usually means the battery is spent. Swap in a fresh battery of the size on the label, press it flat against the contacts, and close the cover. If the chirp continues with a fresh battery seated well, the unit may be at the end of its life and need replacing.
Can I use any battery in a carbon monoxide detector?
No. Use the size and type the label on the unit names, since a battery that does not fit will not sit flat against the contacts. Check the label or the manual before you buy.
How do I know the new battery works?
Press the button on the face of the unit after you fit the battery and close the cover. A beep means the battery is live and the alarm can sound. If the unit stays silent, open the cover and check the battery seating.
What if the detector is wired to the house?
Hardwired detectors with a backup battery usually have a battery door, and the battery can be swapped as in the steps above. Only call a licensed electrician if the unit must be unwired or replaced.
Does a sealed detector have a battery to replace?
No. Sealed long-life units have no replaceable battery. Check the label or the manual, and replace the whole unit on the maker’s replacement date.
Related solar guides
See the best carbon monoxide detectors and the smoke detector sensor types guide. For backup power during an outage, browse the power stations guides.
