Most smoke alarms use 9-volt or AA batteries
The battery your smoke alarm needs depends on the model you own. The two most common types are 9-volt batteries (the rectangular ones with two terminals on top) and AA batteries (the standard cylindrical size). Some older or specialty alarms use 10-year sealed lithium batteries that you cannot replace—those alarms themselves need to be swapped out when the battery dies.
You can find the battery type printed on a label inside the alarm's battery compartment or in the manual that came with it. If you have lost the manual, the model number is usually on the back or bottom of the alarm itself, and you can search that number online to find the specifications.
Most household smoke alarms sold today use either 9-volt or AA, so checking your current alarm takes less than a minute. Open the compartment, look at what is in there, and you will know what to buy next time.
Key Takeaways
- The battery type is printed on a label inside your smoke alarm's battery compartment or in the manual.
- 9-volt and AA batteries are the most common types; some alarms have sealed 10-year batteries that cannot be replaced.
- You can find your alarm's model number on the back or bottom and search online if you cannot locate the manual.
- Replace batteries at least once a year, or when ready if the alarm chirps—that sound means the battery is low.
- Test your alarm monthly by pressing the test button to make sure it still works after you install a new battery.
How to find your smoke alarm's battery compartment
Most smoke alarms have a compartment on the back or side that twists or slides open. Look for a small arrow or the word "battery" printed near the edge. Gently twist or slide in the direction the arrow points until the compartment pops free.
Once it is open, you will see the battery sitting in a plastic holder. The battery itself will be marked with its size—either "9V" or "AA"—printed on the metal casing. If the compartment is stuck, do not force it; a gentle wiggle usually works better than pressure.
If your alarm is mounted on the ceiling, you may need a step stool or ladder to reach it safely. Take your time and do not lean at an angle that puts you off balance.
When to replace your smoke alarm battery
Replace the battery at least once a year, even if the alarm has not made any noise. Many people choose to do this when they change their clocks for daylight saving time, since that is an straightforward date to remember. Mark it on your calendar or set a phone reminder so you do not forget.
If your alarm chirps or beeps every 30 to 60 seconds, that is the low-battery warning. Replace the battery when ready—that sound means the alarm is no longer protecting your home. Do not ignore it or remove the battery to stop the noise; the alarm cannot detect smoke without power.
Some alarms chirp for a few seconds after you install a new battery. That is normal and means the alarm is testing itself. If it continues chirping after a minute, the battery may not be seated properly; open the compartment and press the battery in firmly until you hear a click.
How to install a new battery correctly
Remove the old battery by gently pulling it out of the plastic holder. Note which direction the terminals or flat end faced—the new battery must go in the same way. Most battery holders have a small diagram showing the correct orientation, or you can look at the old battery before you remove it.
Slide the new battery into the holder, making sure it sits flat and the terminals or flat end match the diagram. You should feel a slight resistance as it slides in; that is normal. Close the battery compartment by twisting or sliding it back into place until it clicks.
Press the test button on the front of the alarm. You should hear a loud beep or alarm sound for a few seconds. If you hear nothing, open the compartment again and check that the battery is fully seated. If it still does not work, the alarm itself may be faulty and need replacement.
Buying the right replacement battery
When you go to buy a new battery, bring the old one with you or write down the size—either "9V" or "AA"—on a piece of paper. This takes the guesswork out of shopping and prevents you from buying the wrong size by mistake.
Standard alkaline batteries work fine for smoke alarms and are the cheapest option. You can buy them at any grocery store, pharmacy, hardware store, or online retailer. A single 9-volt battery costs between $3 and $8, and AA batteries usually cost $1 to $3 each, depending on the brand and where you shop.
Do not buy rechargeable batteries for your smoke alarm. Rechargeable batteries lose their charge over time even when not in use, and a smoke alarm needs to work reliably at full power whenever smoke is present.
Why some alarms have batteries you cannot replace
Newer smoke alarms often come with sealed 10-year lithium batteries built inside. These batteries are designed to last the entire life of the alarm, so you never have to open a compartment or buy replacements. When the 10 years are up, you throw away the entire alarm and install a new one.
These sealed-battery alarms are convenient because you do not have to remember to replace batteries every year. However, they cost more upfront—usually $25 to $50 per alarm instead of $10 to $20 for a battery-powered model. If you prefer the simplicity and do not mind replacing the whole alarm after 10 years, they are a good choice.
You can tell if your alarm has a sealed battery by looking for text that says "10-year battery" or "sealed battery" on the packaging or the back of the alarm. If you open the compartment and see no removable battery, that alarm has a sealed battery and cannot be serviced at home.
Troubleshooting when your alarm will not stop chirping
If your alarm chirps even after you install a fresh battery, the battery may not be making good contact with the terminals. Open the compartment, remove the battery, and wipe both the battery terminals and the metal contacts inside the holder with a dry cloth. Reinsert the battery and close the compartment firmly.
If it still chirps, the alarm itself may be faulty. Smoke alarms typically last 8 to 10 years, and a chirping alarm that does not stop after a new battery is installed is often a sign that the alarm has reached the end of its life. You will need to replace the entire unit.
Do not ignore a chirping alarm or remove the battery to silence it. A silent alarm cannot protect you. If the alarm is faulty, buy a replacement as soon as you can.
Frequently Asked Questions
Can I use a different battery size than what my alarm calls for?
No. Using the wrong battery size will not fit the holder properly, and the alarm will not work. Always use the exact size printed on the label inside your alarm's compartment. If you are unsure, check the model number online or call the manufacturer.
How long does a battery last in a smoke alarm?
A standard alkaline 9-volt or AA battery lasts about one year in a smoke alarm, though this varies depending on the alarm model and how often it tests itself. Replace the battery once a year regardless of whether you hear a chirp, because some alarms do not warn you until the battery is nearly dead.
What should I do with the old battery after I remove it?
Take used batteries to a recycling center, hardware store, or electronics retailer that accepts batteries. Many stores like Home Depot and Best Buy have battery recycling bins near the entrance. Do not throw batteries in the trash, as they contain materials that should be recycled.
Why does my alarm chirp a few seconds after I put in a new battery?
That chirp is the alarm testing itself to confirm the new battery is working. It should stop after a few seconds. If it continues chirping every 30 to 60 seconds, the battery is not seated properly or is faulty. Remove it, check the contacts, and try again.
Do I need to turn off the power to my alarm before replacing the battery?
If your alarm is hardwired to your home's electrical system, you do not need to turn off the power to replace the battery. The battery is a backup, and the alarm will continue to work on electricity while you swap it. If your alarm is battery-only, there is no power switch to worry about.