Most smoke alarms use 9-volt or AA batteries, depending on the model

The battery type your smoke alarm needs depends on which model you own. The two most common are 9-volt batteries (the rectangular ones) and AA batteries (the cylindrical ones). A few older or specialty models use 10-year sealed batteries that cannot be replaced. Check the label on the back or inside the battery compartment of your alarm — it will say exactly which type to buy.

The label also tells you the brand and model number, which is useful if you need to order a replacement alarm later. Take a photo of that label with your phone so you have it when you are at the store or shopping online.

Key Takeaways

  • Check the label inside your smoke alarm's battery compartment to find out whether it uses 9-volt or AA batteries.
  • Replace the battery once per year, or when ready when the alarm chirps — that chirp means the battery is low.
  • Use a fresh battery from a sealed package, not one that has been sitting in a drawer for months.
  • Some smoke alarms have a sealed 10-year battery that cannot be replaced; when it dies, you replace the entire alarm.

How to find out which battery your alarm uses

Open the battery compartment on your smoke alarm. Most models have a small door or cover that slides or clips off. Inside, you will see either a 9-volt battery (shaped like a small rectangular block with two round terminals on top) or one or two AA batteries (shaped like a cylinder about the size of your pinky finger).

If you cannot open the compartment or do not see a battery, your alarm may have a sealed 10-year battery built in. Look for text on the alarm that says "10-year battery" or "sealed battery." If it has one, you cannot replace just the battery — you will need to replace the entire alarm when it stops working.

When to replace the battery

Replace your smoke alarm battery once per year, even if the alarm has not chirped. Many people set a reminder on their phone for the same day they change their clocks for daylight saving time, since that happens twice a year and is straightforward to remember. If you live somewhere that does not observe daylight saving time, pick any date that matters to you — your birthday, New Year's Day, or the first day of spring.

If your alarm chirps or beeps every 30 to 60 seconds, that is the low-battery warning. Replace the battery when ready, even if it is not your scheduled replacement date. That chirp means the battery is too weak to power the alarm if there is a fire.

How to replace the battery safely

Turn off the alarm before you open it. Most models have a button or switch on the face that silences the alarm temporarily. Press it and hold it for a few seconds. This prevents the alarm from sounding while you work.

Open the battery compartment and remove the old battery. Note which way the positive and negative terminals face — usually there is a label or diagram inside the compartment showing the correct direction. Insert the new battery the same way, making sure it sits flat and the terminals make contact. Close the compartment.

Press the test button on the alarm to make sure it works. You should hear a loud beep. If you hear nothing, open the compartment again and check that the battery is seated correctly and facing the right direction.

What type of battery to buy

Buy fresh batteries from a sealed package, not loose ones from a drawer or a bin at a store. Batteries lose charge over time, even when they are not being used. A battery that has been sitting around for a year or more may not last as long as a new one.

For 9-volt alarms, buy 9-volt batteries. For AA alarms, buy AA batteries. Do not try to use a different size or type — it will not fit, or it will not power the alarm correctly. Alkaline batteries (the standard kind you find in most stores) work fine for smoke alarms. You do not need rechargeable or specialty batteries.

Buy enough batteries to replace all the smoke alarms in your home at the same time. Most homes have at least one on each floor, and one in each bedroom. Replacing them all on the same day means you will not forget which ones you have already done.

Why your alarm might still chirp after you replace the battery

If the alarm keeps chirping after you put in a new battery, the battery may not be making good contact with the terminals. Open the compartment again and remove the battery. Wipe the metal terminals on the battery and inside the compartment with a dry cloth to remove any dust or corrosion. Reinsert the battery and test again.

If it still chirps, try a different new battery. The first one may have been defective. If a second new battery does not stop the chirping, the alarm itself may be failing and may need to be replaced. Chirping that continues after you have tried two fresh batteries is a sign the alarm's internal circuitry is wearing out.

Sealed 10-year batteries and when to replace the whole alarm

Some smoke alarms come with a sealed 10-year battery that is built in and cannot be removed. These alarms are designed to work for 10 years without any maintenance, then be thrown away and replaced. When the battery dies, the entire alarm stops working.

If your alarm has a sealed battery, mark the installation date on the alarm itself with a permanent marker so you remember when to replace it. After 10 years, remove the alarm and install a new one. Do not try to open a sealed alarm or replace the battery inside — the alarm is designed as a single unit.

Frequently Asked Questions

Can I use a rechargeable battery in my smoke alarm?

Rechargeable batteries are not recommended for smoke alarms. They lose charge faster than alkaline batteries, even when the alarm is not in use. A rechargeable battery that has lost charge will not power the alarm if there is a fire. Stick with fresh alkaline batteries from a sealed package.

What should I do with the old battery?

Take old batteries to a recycling center or a store that accepts battery recycling. Many hardware stores and electronics retailers have battery drop-off bins near the entrance. Do not throw batteries in the trash — they contain materials that can harm the environment.

How do I know if my alarm has a 10-year battery?

Look at the alarm itself. If you see text that says "10-year battery," "sealed battery," or "non-replaceable battery," it has a built-in battery you cannot change. If you can open a compartment and see a removable battery inside, you can replace it yourself.

Can I use a 9-volt battery in an alarm that takes AA batteries?

No. A 9-volt battery is larger and will not fit in a compartment designed for AA batteries. Using the wrong size battery can damage the alarm or cause it to malfunction. Always use the exact battery type your alarm's label specifies.

What if I cannot find the battery compartment?

Some alarms have the compartment on the side or back instead of the bottom. Look for a small door, cover, or slot. If you still cannot find it, check the user manual or search online for the alarm's model number. If the alarm truly has no visible compartment, it likely has a sealed 10-year battery.