Replace the battery by opening the alarm cover, sliding out the old battery, and inserting a new one of the same type
Most First Alert smoke alarms use a 9-volt battery that slides into a clip inside the unit. The process takes less than a minute: open the cover, remove the old battery, insert the new one, and close the cover. The alarm will chirp once when power is restored, confirming the battery is seated correctly.
Some First Alert models use two AA batteries instead. These sit in a battery compartment behind a small door on the front or side of the alarm. The steps are the same — open, remove, insert new batteries in the correct direction, close — but you will replace two cells instead of one.
Before you start, check the model number on the back of your alarm. It is usually printed on a sticker. Knowing the model tells you which battery type your alarm needs, and you can buy the right one before you climb the ladder.
Key Takeaways
- First Alert alarms use either a single 9-volt battery or two AA batteries, depending on the model.
- The battery compartment is usually on the front or side of the alarm and opens by sliding or unclipping the cover.
- Insert the new battery or batteries in the same direction the old ones faced — the positive and negative terminals must align with the clips.
- The alarm will chirp once when the new battery makes contact, which means it is working.
- Replace the battery as soon as the alarm chirps regularly, because a weak battery will not power the alarm during a fire.
Locate the battery compartment on your alarm
The battery compartment is almost always on the front or side of the alarm, not the back. On most First Alert models, you will see a small seam or a clip that marks the edge of a removable cover. Some covers slide downward; others unclip by pressing a small tab on the side.
If your alarm is mounted on the ceiling, you may need a step ladder to reach it safely. Do not stand on a chair or stretch from a ladder rung — climb to a stable position where you can use both hands. The battery swap itself is quick, but a fall is not worth the risk.
If you cannot find the compartment, check the model number on the back of the alarm and search the First Alert website for the manual. The manual will show you exactly where the compartment is and how to open it.
Remove the old battery and note its type
Once the cover is open, you will see the battery sitting in a plastic clip or holder. For a 9-volt battery, the clip holds it at an angle. For AA batteries, they sit upright in a plastic tray with metal contacts at the top and bottom.
Gently pull the 9-volt battery out of the clip, or slide the AA batteries straight up and out of their slots. Do not force them — if a battery is stuck, wiggle it slightly side to side as you pull. Look at the battery terminals (the metal bumps or flat ends) and note which direction they faced. The new battery must go in the same way.
If the battery is leaking or corroded, wipe the inside of the compartment with a dry cloth before inserting the new one. Corrosion looks like white or blue powder around the battery contacts and can prevent the new battery from making good contact.
Insert the new battery in the correct direction
Buy a new battery of the same type — a 9-volt if your alarm used a 9-volt, or two AA batteries if it used AA. The battery type is printed on the old battery itself, and you can also find it in the alarm manual or on the First Alert website by searching your model number.
Slide or place the new battery into the compartment in the same direction the old one faced. For a 9-volt, the clip will guide it into the correct position — the positive terminal (marked with a plus sign) should face the clip's metal contact. For AA batteries, the positive end (the flat or slightly raised end) should face upward toward the metal contacts at the top of the tray.
Push the battery in firmly until you hear or feel a click. The clip should hold it snugly. If the battery is loose, it will not make good contact and the alarm will not work.
Close the cover and listen for the confirmation chirp
Slide or clip the cover back into place. You should hear a single chirp from the alarm within a few seconds. This chirp means the battery is making contact and the alarm has power. If you do not hear a chirp, open the cover again and check that the battery is seated correctly and facing the right direction.
If the alarm still does not chirp after you reseat the battery, the battery itself may be dead. Try a fresh battery from a different package. Batteries can fail before their expiration date, especially if they have been stored in a hot or damp place.
Once you hear the chirp, the job is done. The alarm is now powered and will sound if it detects smoke.
When to replace the battery before it dies
Most First Alert alarms will chirp once every 30 to 60 seconds when the battery is running low. This chirp is different from the alarm sound — it is a single short beep, not a loud wailing sound. When you hear this pattern, replace the battery within a few days.
Do not wait until the chirping becomes constant or until the alarm stops chirping altogether. A dead battery means the alarm cannot detect smoke, and you will have no warning in a fire. Keep spare batteries on hand so you can swap them out when ready when the low-battery chirp starts.
Write the replacement date on the new battery with a permanent marker. This helps you remember when you last changed it and makes it easier to spot an old battery if you find one loose in a drawer later.
Troubleshooting if the alarm still does not work
If the alarm does not chirp after you insert a fresh battery, check that the battery is the correct type for your model. A 9-volt battery will not work in an alarm designed for AA batteries, and vice versa. The compartment will not close properly if you have the wrong battery, which is usually a sign something is wrong.
If the battery is correct and seated firmly but the alarm still does not chirp, the alarm itself may have failed. First Alert alarms typically last 5 to 10 years. If your alarm is older than that and has not been replaced, a new battery will not fix it — you will need to replace the entire unit.
If the alarm chirps once when you insert the battery but then stops working, the battery may be defective. Remove it and try a different new battery from a different package or brand. If a second battery also fails to power the alarm, the alarm unit is likely faulty and should be replaced.
Frequently Asked Questions
What type of battery does my First Alert smoke alarm use?
Most First Alert alarms use either a single 9-volt battery or two AA batteries. Check the model number on the back of your alarm and search the First Alert website, or look inside the battery compartment — the shape and size of the slot will tell you which type you need. The old battery itself will also show you the correct type.
How often should I replace the battery?
Replace the battery when the alarm chirps regularly — usually once every 30 to 60 seconds. This chirp means the battery is low. In general, a battery lasts 6 to 12 months, but this varies based on the alarm model and how often it is used. Some alarms chirp more frequently than others.
Can I use a rechargeable battery in my First Alert alarm?
Most First Alert alarms are designed for single-use alkaline batteries and may not work reliably with rechargeable batteries. Rechargeable batteries have a different voltage curve and may not trigger the low-battery chirp at the right time. Stick with alkaline 9-volt or AA batteries unless your alarm manual specifically says rechargeable batteries are safe.
Why is my alarm still chirping after I put in a new battery?
The alarm may be chirping for a reason other than low battery — some models chirp to signal a malfunction or to remind you to test the unit. Press and hold the test button on the front of the alarm for a few seconds. If the alarm sounds loudly, the unit is working. If the chirping continues, consult the manual for your specific model.
Do I need to turn off the alarm before changing the battery?
No. Removing the battery will cut power to the alarm, so there is nothing to turn off. The alarm will not sound while the battery is out. Once you insert the new battery, the alarm will power back on and chirp once to confirm it is working.