Replace the battery by opening the alarm cover, removing the old battery, and inserting a new one of the same type

Most First Alert smoke alarms use a 9-volt battery that slides or clips into a holder inside the unit. The whole job takes about two minutes. Open the cover by twisting it counterclockwise or unclipping the sides — the method depends on your model — then locate the battery compartment. Remove the old battery by gently pulling it straight out, note which way the terminals face, and slide the new battery in the same direction. Close the cover, press the test button to confirm the alarm sounds, and you are done.

The battery type matters. First Alert alarms almost always use a 9V battery, but some models use AA or AAA instead. Check the label on the back or inside the cover before you buy a replacement. If you cannot find the label, bring the old battery to a hardware store and match it by size and terminal type.

Key Takeaways

  • Most First Alert smoke alarms hold a single 9-volt battery that you can access by twisting or unclipping the cover.
  • Remove the old battery by pulling it straight out, then insert the new battery with the terminals facing the same direction.
  • Test the alarm when ready after replacing the battery by pressing the test button — you should hear a loud chirp or alarm sound.
  • If your alarm chirps once every 30 to 60 seconds after you install a new battery, the battery may be low or installed backward.

Locate the battery compartment on your specific model

First Alert makes several alarm styles, and the cover design varies. Some models have a cover that twists counterclockwise like a jar lid. Others have a clip or latch on one or both sides that you press inward to release the cover. A few models have a sliding cover that moves downward. Look at the seam where the cover meets the body of the alarm and follow the shape — you will see which method applies.

If the cover is stuck, do not force it. A stuck cover usually means the alarm is old and the plastic has warped slightly. Try twisting very gently in both directions to find the point where it gives, or use a plastic spoon handle to explore even pressure around the edge. If the cover cracks, you will need to replace the entire alarm.

Remove and replace the battery correctly

Once the cover is open, you will see the battery holder — a plastic clip or socket with two metal terminals. The battery slides or clips in one direction only. Before you remove the old battery, look at which terminal (the raised metal bump) points toward which side of the holder. This matters because batteries work only one way.

Pull the old battery straight out. Do not twist it or rock it side to side, as this can damage the terminals. If the battery is stuck, it may have corroded slightly. Let it sit for a minute, then try again with steady, even pressure. Once the old battery is out, insert the new one with the same terminal orientation — the positive terminal (usually marked with a plus sign) should face the same direction as it did before.

Push the new battery in firmly until you hear or feel a click. The battery should sit flush in the holder with no gaps. If it does not click or feels loose, remove it and try again, making sure the terminals are aligned with the metal contacts inside the holder.

Test the alarm after installation

Press and hold the test button on the front of the alarm for three to five seconds. You should hear a loud chirp or a full alarm sound — the noise confirms the battery is installed correctly and the alarm is working. If you hear nothing, the battery may be installed backward or may be defective. Remove it, flip it around, and test again.

After the test, the alarm should be silent. If it chirps once every 30 to 60 seconds, the battery is low or not making good contact with the terminals. Remove the battery, wipe the terminals with a dry cloth, and reinstall it. If the chirping continues, the battery may be defective — try a fresh one from a different package.

Know when to replace the entire alarm instead

If the alarm is more than ten years old, replacing the battery may not be worth your time. First Alert alarms have a lifespan of about ten years, after which the sensors degrade and the unit becomes less reliable. Check the date printed on the back of the alarm. If it is older than 2014, consider replacing the whole unit rather than buying batteries for it.

Also replace the alarm if the cover is cracked, if the battery holder is corroded or damaged, or if the test button does not produce a sound even after you have tried a fresh battery. These are signs the alarm has reached the end of its life. A new alarm costs between fifteen and forty dollars and will protect your home more reliably than an aging unit.

Battery types and where to buy them

A 9-volt battery costs two to four dollars at a hardware store, drugstore, or supermarket. Duracell and Energizer are the most common brands, and either works fine in a First Alert alarm. Some stores sell multi-packs of 9V batteries at a lower per-unit price if you have multiple alarms in your home.

If your model uses AA or AAA batteries, the cost is similar but the pack sizes are larger. Buy alkaline batteries, not rechargeable ones — rechargeable batteries discharge faster and may not power the alarm reliably. Store extra batteries in a cool, dry place. Do not store them in the alarm itself unless you are actively using them, as batteries can leak if left unused for months.

Frequently Asked Questions

How often should I replace the battery in a First Alert smoke alarm?

Replace the battery once a year, ideally on the same day each year — many people do it when they change their clocks for daylight saving time. If the alarm chirps once every 30 to 60 seconds, the battery is low and needs replacement when ready, even if less than a year has passed.

What if the battery is stuck and I cannot remove it?

Do not pull hard, as you can damage the battery holder. Let the alarm sit for a few minutes, then try again with steady, even pressure. If it is still stuck, the battery may have corroded. Wipe the battery and the holder with a dry cloth and try once more. If it remains stuck, the alarm is likely too old to repair safely.

Can I use a rechargeable battery in my First Alert alarm?

Rechargeable batteries discharge faster than alkaline ones and may not power the alarm long enough to be reliable. Use a standard alkaline 9-volt, AA, or AAA battery instead. Rechargeable batteries are better for devices you use frequently, not for safety equipment.

Why does my alarm still chirp after I put in a new battery?

The battery may be installed backward — remove it and flip it around so the terminals face the opposite direction. If it still chirps, the new battery may be defective. Try a battery from a different package. If a third battery also chirps, the alarm itself may be failing and should be replaced.

Is it safe to leave a First Alert alarm without a battery while I shop for a replacement?

No. An alarm without a battery cannot detect smoke and will not alert you to a fire. Replace the battery the same day you remove the old one, or keep a spare battery on hand so you can swap it in when ready.