How to Change the Battery in a Kidde Carbon Monoxide and Smoke Alarm

Open the alarm and locate the battery compartment

Most Kidde combination carbon monoxide and smoke alarms have a battery compartment on the back or bottom of the unit. Look for a small door or panel — it usually slides or pops open without tools. If your model is mounted on the ceiling, you will need a step ladder to reach it safely.

Once you have the alarm in hand, examine the back and bottom edges for a seam or a small arrow pointing to "open" or "battery." Some models have a compartment door that slides toward the center of the unit; others have a hinged door that swings down. If you cannot locate it visually, check the manual that came with your alarm — Kidde includes a diagram showing exactly where the battery sits.

Remove the old battery and note its size

Open the compartment fully and look at the battery already inside. Most Kidde combination alarms use a 9-volt battery, which is rectangular and about the size of a lighter. Some older or smaller models may use AA or AAA batteries instead. The battery will be held in place by a plastic clip or a wire connector.

If the battery is held by a clip, gently push or slide the clip away from the battery and lift it out. If it is connected by wires, note which wire connects to the positive (+) terminal and which connects to the negative (−) terminal before you disconnect them — or take a photo with your phone so you can reconnect the new battery the same way. Write down the battery size (9V, AA, or AAA) before you go to the store.

Key Takeaways

Most Kidde combination alarms use a 9-volt battery, but check your manual or the old battery to be sure before you buy a replacement.
The battery compartment is usually on the back or bottom of the unit and opens by sliding or popping a small door without tools.
When you remove the old battery, note which wire or clip connects to the positive and negative terminals so you can reconnect the new one correctly.
After you install the new battery, press the test button on the alarm to confirm it is working — you should hear a loud beep or alarm sound.
If the alarm does not beep after you install the new battery, remove it, wait 30 seconds, and reinstall it to reset the connection.

Buy the correct replacement battery

Take the battery size you noted to a hardware store, pharmacy, or supermarket. Kidde alarms work with standard batteries sold everywhere — you do not need a special brand or a Kidde-branded battery. A 9-volt battery costs between $5 and $10 depending on the brand and whether you buy a single battery or a pack.

If you are not sure which size you need, bring the old battery with you or take a photo of it on your phone and show it to a store employee. They can match it when ready. Alkaline batteries (the most common type) last longer than carbon-zinc batteries, so choose alkaline if the price difference is small.

Install the new battery and reconnect the wires

Insert the new battery into the compartment in the same direction the old one faced. If the battery is held by a clip, slide the clip back over the battery until it clicks or snaps into place. If the battery connects by wires, reconnect the positive wire to the positive terminal and the negative wire to the negative terminal — the terminals are usually marked with a + and − symbol on the battery itself.

Push the battery compartment door closed until you hear or feel it latch. Do not force it; if it does not close smoothly, remove the battery and check that it is seated correctly in the compartment. Once the door is closed, the alarm should be ready to test.

Test the alarm to confirm the battery is working

Locate the test button on the front or side of the alarm — it is usually labeled "test" and is slightly recessed so you cannot press it by accident. Press and hold the button for 3 to 5 seconds. You should hear a loud beeping sound or alarm chirp. If the alarm is a combination unit, it may beep once for the smoke sensor and once for the carbon monoxide sensor.

If you hear nothing, remove the battery, wait 30 seconds, and reinstall it. Then press the test button again. If the alarm still does not beep, the battery may be defective or installed incorrectly. Remove it, check that the wires or clip are connected properly, and try again. If it still does not work after a second attempt, the alarm itself may be faulty and may need to be replaced.

Reset the alarm if it chirps after battery installation

Some Kidde alarms chirp once every 30 to 60 seconds after a battery change — this is normal and means the alarm is resetting itself. The chirping should stop within a few minutes. If it continues for more than 10 minutes, remove the battery, wait one full minute, and reinstall it.

If the alarm chirps continuously even after you reset it, the unit may be detecting a problem — for example, a low battery in a wireless sensor or a fault in the smoke or carbon monoxide chamber. Check the manual for a list of what different chirp patterns mean. If you cannot resolve it, contact Kidde customer service or replace the alarm.

Know when to replace the entire alarm instead of just the battery

Kidde smoke and carbon monoxide alarms have a lifespan of 5 to 10 years depending on the model. If your alarm is more than 10 years old, the sensors inside may no longer be reliable even if the battery is new. Check the date printed on the back of the unit — if it is older than 2014 or 2015, consider replacing the whole alarm rather than just the battery.

If the alarm fails the test even after you install a fresh battery and reset it twice, the sensors may be worn out. Kidde alarms are not repairable — you will need to buy a new one. A new combination smoke and carbon monoxide alarm costs between $25 and $60 depending on the features and brand.

Frequently Asked Questions

What type of battery does a Kidde combination alarm use?

Most Kidde combination smoke and carbon monoxide alarms use a 9-volt battery. Some models use AA or AAA batteries instead. Check the compartment or the manual to see which size your alarm needs before you buy a replacement.

How often do I need to change the battery?

A 9-volt alkaline battery in a Kidde alarm typically lasts 6 to 12 months depending on how often the alarm tests itself and whether it has detected any smoke or carbon monoxide. If the alarm chirps once every 30 to 60 seconds, the battery is low and needs to be replaced soon.

Can I use a rechargeable battery in my Kidde alarm?

No. Kidde alarms are designed for single-use alkaline batteries. Rechargeable batteries have a different voltage and may not power the alarm reliably or may drain too quickly. Always use a new alkaline battery.

What if the alarm beeps after I install the new battery?

A single beep or chirp after battery installation is normal and means the alarm is resetting. If it chirps continuously every 30 to 60 seconds for more than 10 minutes, remove the battery, wait one minute, and reinstall it. If the chirping continues, the alarm may have detected a fault and may need to be replaced.

Do I need to turn off power to the alarm before changing the battery?

If your Kidde alarm is hardwired to your home's electrical system, it has a backup battery. You do not need to turn off power — straightforward open the compartment and change the battery while the alarm is still mounted. If you are uncomfortable working near electrical wiring, turn off the breaker to that circuit first.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.