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 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 clip. Slide the old battery out, note which way the terminals face, and slide the new battery in with the terminals pointing the same direction. Close the cover and test the alarm by pressing the test button for three seconds until you hear the horn.

The most common mistake is inserting the battery backward. The positive and negative terminals must match the clip orientation, or the alarm will not sound. If the alarm does not chirp during the test, remove the battery, wait ten seconds, and reinsert it. If it still does not work, the battery may be defective or the alarm itself may have reached the end of its life (most units last ten years).

Key Takeaways

  • First Alert smoke alarms typically use 9-volt batteries that slide into a clip inside the cover.
  • Open the cover by twisting counterclockwise or unclipping the sides, depending on your model.
  • Insert the new battery with the terminals facing the same direction as the old one.
  • Press the test button for three seconds after closing the cover to confirm the alarm works.
  • If the alarm does not sound during the test, remove the battery, wait ten seconds, and reinsert it.

Locate the battery compartment

The battery compartment is inside the alarm cover. To reach it, you need to open the cover first. Most First Alert models use one of two methods: twist the cover counterclockwise until it releases, or look for small clips or tabs on the sides of the cover and press them inward while pulling the cover away from the base.

If you are not sure which method your model uses, check the back or bottom of the alarm for a label with the model number. You can also look at the inside of the cover once you have it partially open—if you see clips, press them. If the cover does not budge with gentle pressure, you are likely twisting the wrong direction; try clockwise instead.

Remove the old battery

Once the cover is open, you will see a battery clip—a plastic or metal holder with two metal terminals. The old battery slides into this clip horizontally. Grip the battery by its sides and pull it straight out toward you. Do not touch the terminals with your bare fingers if possible, as oils can interfere with the connection, though this is rare with 9-volt batteries.

Before you throw the old battery away, note which terminal (the raised metal nub) faces up or toward the front of the alarm. This matters because the new battery must go in the same way. If you forget, the alarm will not work and you will have to remove and flip the battery.

Insert the new 9-volt battery

Buy a fresh 9-volt battery from any grocery store, pharmacy, or hardware store. Duracell, Energizer, and First Alert's own brand all work equally well in First Alert alarms. Hold the new battery so the terminals face the same direction as the old one did, then slide it into the clip. You should feel a slight click or resistance as it seats fully.

Push the battery all the way in until it stops. If it does not slide smoothly, remove it and check that the terminals are facing the right direction. Forcing a backward battery can bend the clip or damage the terminal connection. Once the battery is seated, close the cover by twisting it clockwise or pressing the clips back into place, depending on your model.

Test the alarm after battery replacement

Press and hold the test button on the front of the alarm for three seconds. The test button is usually a round or square button in the center of the cover. You should hear a loud horn sound—this confirms the alarm is working and the battery is making good contact. The horn will stop when you release the button.

If you hear nothing, remove the cover again and check that the battery is fully seated in the clip. Remove the battery, wait ten seconds, and reinsert it. Then test again. If the alarm still does not sound, the battery may be dead (even though it is new), or the alarm itself may have failed. Try a different battery if you have one on hand. If a second battery does not work, the alarm has likely reached the end of its service life and should be replaced.

When to replace the entire alarm instead of just the battery

First Alert smoke alarms are designed to last about ten years. If your alarm is older than that, replacing the battery may not help—the sensor inside degrades over time and stops detecting smoke reliably. Check the date printed on the back or bottom of the unit. If it says 2014 or earlier, buy a new alarm rather than a new battery.

You should also replace the entire alarm if the test button does not produce a sound even after you have tried two fresh batteries. A working alarm is more important than saving the cost of a new unit. Most hardware stores sell First Alert alarms for under thirty dollars, and installation takes less than five minutes.

Frequently Asked Questions

What type of battery does a First Alert smoke alarm use?

Most First Alert smoke alarms use a standard 9-volt battery. Check the label on the back or inside the cover to confirm, as a few older models may use different sizes. The battery compartment will also show you the correct size if you look at the clip shape.

How often should I replace the battery?

Replace the battery once a year, or whenever the alarm chirps every 30 to 40 seconds. The chirp is the alarm's way of telling you the battery is low. Do not ignore it—a low battery means the alarm cannot sound if there is a fire. Many people replace batteries on the same day they change their clocks for daylight saving time, which makes it straightforward to remember.

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

No. First Alert alarms are designed for single-use alkaline 9-volt batteries. Rechargeable batteries have different voltage output and may not trigger the alarm reliably. Always use a fresh alkaline battery from a major brand.

Why does my alarm keep chirping even after I put in a new battery?

The chirp may continue for a few minutes after you insert the battery as the alarm resets. If it chirps longer than that, remove the battery, wait 30 seconds, and reinsert it. If the chirping does not stop within a minute, the alarm may have a different problem—dust in the sensor, a wiring issue, or an internal fault. Try cleaning the vents with a vacuum hose, but if that does not work, replace the alarm.

Is it safe to test the alarm indoors?

Yes. The test button produces a loud sound, but it is safe to press indoors. The noise is designed to be loud enough to wake you in a fire, so expect it to be startling. Press the button during the day when you are prepared for the sound, and warn anyone else in the house before you test.