Most smoke detectors use 9-volt or AA batteries

The battery your smoke detector needs depends on the model you own. The two most common types are 9-volt batteries (the rectangular ones with terminals on top) and AA batteries (the cylindrical ones). Some detectors use two AA batteries instead of one 9-volt. A few older or specialty models use 10-year lithium batteries that you cannot replace—the whole detector is meant to be thrown away and replaced after ten years.

Check the label on the back or side of your detector to see which type it takes. The label will say "9V" or "AA" or show a picture of the battery. If you cannot find the label, open the battery compartment and look at the size and shape of the slot—that will tell you what fits.

Buy the same brand and type that came out of your detector. Alkaline batteries (the standard kind sold everywhere) work fine for smoke detectors and cost a few dollars each. Do not use rechargeable batteries in a smoke detector unless the manual specifically says they are safe—rechargeable batteries can lose charge over time and leave your detector without power when you need it.

Key Takeaways

  • Check the label on your detector or look inside the battery compartment to find out whether it takes a 9-volt or AA battery.
  • Replace batteries with the same type and brand that came out, using standard alkaline batteries.
  • Do not use rechargeable batteries unless your detector's manual says they are safe.
  • Replace batteries once a year, or whenever your detector beeps to signal low battery.
  • Some detectors have 10-year lithium batteries built in and cannot be replaced—the whole unit is discarded after ten years.

When to replace your smoke detector batteries

Replace batteries once a year, even if the detector has not beeped. A good habit is to change them when you change your clocks for daylight saving time—that gives you a built-in reminder twice a year. Mark it on your calendar or set a phone reminder so you do not forget.

Your detector will also beep or chirp every 30 to 60 seconds when the battery is low. That beep means replace the battery now, not later. A low battery leaves your detector unable to sound an alarm if there is a fire. If your detector is beeping and you replace the battery but it keeps beeping, the detector itself may be faulty and need to be replaced.

How to replace the battery safely

Turn off power to the detector if it is hardwired to your home's electrical system. If you are not sure whether it is hardwired, look for a wire coming out of the back—if there is one, turn off the breaker for that circuit at your electrical panel. If the detector runs on batteries only, you do not need to turn off anything.

Open the battery compartment. Most detectors have a clip or a small door on the side or back. Gently pull out the old battery and note which way the positive and negative ends face. Insert the new battery the same way—positive end toward the spring or contact marked with a plus sign.

Close the compartment and press the test button on the front of the detector. You should hear a loud alarm sound for a few seconds. If you hear nothing, the battery may not be seated properly—open the compartment again and make sure it is pushed all the way in. If it still does not work after you reseat the battery, the detector may need to be replaced.

Why your detector might still beep after a battery change

If your detector keeps beeping after you put in a new battery, the problem is usually one of three things: the battery is not fully seated in the compartment, the detector is too old and needs replacement, or there is dust or debris inside blocking the sensor.

First, open the compartment again and push the battery all the way in until you hear or feel a click. Press the test button. If it still beeps, try a different new battery from a different package—sometimes a battery from the store is defective.

If a fresh battery from a new package still does not stop the beeping, the detector itself has likely reached the end of its life. Most smoke detectors last 8 to 10 years. If yours is older than that, replace the whole unit. If it is newer, you can try gently vacuuming around the vents with a brush attachment, but if that does not work, replacement is the safest choice.

Hardwired detectors and battery backup

Some smoke detectors are wired directly into your home's electrical system but also have a battery backup. The battery powers the alarm if the power goes out. These detectors need a battery replacement on the same schedule as battery-only models—once a year or whenever they beep.

If you have a hardwired detector with battery backup, turn off the breaker for that circuit before you open the compartment. Wait a few seconds to make sure the power is off, then proceed with the battery replacement the same way you would for a battery-only detector. Turn the breaker back on when you are done.

Storing extra batteries and disposal

Keep a spare 9-volt or AA battery (whichever your detector uses) in a drawer or cabinet near your detectors so you have one on hand when you need it. Do not store batteries loose in a junk drawer where they might touch metal objects—that can cause them to discharge or overheat.

When you remove an old battery, do not throw it in the trash. Take it to a battery recycling program. Many hardware stores, electronics retailers, and municipal hazardous waste facilities accept used batteries for free. Check Earth911.com or call your local waste management office to find a drop-off location near you.

Frequently Asked Questions

Can I use a different brand of battery than what came in the detector?

Yes. Any standard alkaline 9-volt or AA battery will work, regardless of brand. Duracell, Energizer, Amazon Basics, and store brands all work the same way in a smoke detector. Buy whatever is cheapest or most available.

What if my detector takes batteries I cannot find in stores?

If your detector takes an unusual battery size, you can order it online from Amazon, eBay, or a battery specialty retailer. You can also replace the detector with a newer model that uses common 9-volt or AA batteries, which are sold everywhere.

Do I need to press the test button after I put in a new battery?

Yes. Press and hold the test button for a few seconds. You should hear a loud alarm. This confirms the battery is installed correctly and the detector is working. If you hear nothing, reseat the battery and try again.

Is it safe to leave a smoke detector without a battery while I wait to buy a new one?

No. A detector without a battery cannot sound an alarm if there is a fire. Replace the battery the same day you discover it is low or missing. If you do not have a battery on hand, buy one before the sun sets.

How long does a 9-volt battery last in a smoke detector?

A fresh alkaline 9-volt battery typically lasts 6 to 12 months in a smoke detector, depending on the model and how often the detector tests itself. This is why replacing batteries once a year is the standard recommendation.