How to Change a First Alert Smoke Alarm Battery

Replace the battery in under two minutes

Most First Alert smoke alarms use a 9-volt battery that slides out from the front or back of the unit. Open the alarm cover by pressing the tab or twisting the cover counterclockwise, depending on your model. Remove the old battery by pulling it straight out, then slide a fresh 9-volt battery into the connector until it clicks. Close the cover and press the test button to confirm the alarm sounds.

The whole job takes less than two minutes. You do not need tools, and you do not need to turn off power to your home. If your alarm is hardwired to your electrical system, it will have a backup battery that works the same way — changing the backup battery does not affect the hardwired power.

Key Takeaways

First Alert smoke alarms typically use a 9-volt battery that you can replace by opening the cover and sliding the old battery out.
Most models have a tab or twist-lock cover; check your specific model number on the back of the unit if you are unsure which type you have.
Press the test button after installing the new battery to confirm the alarm sounds and the battery is seated correctly.
Hardwired alarms with backup batteries work the same way — the backup battery change does not interrupt your home's electrical connection.
Replace batteries once a year, or when ready if the alarm chirps every 30 to 40 seconds, which signals a low battery.

Locate the battery compartment on your model

First Alert makes several smoke alarm designs, and the battery location varies slightly. Most models have the battery compartment on the front face of the unit, behind a removable cover. Some older or specialty models have the battery on the back. Check the model number printed on the back of your alarm — it usually starts with "SA" or "SC" — and look for a label or diagram showing where the battery sits.

If you cannot find a label on the unit itself, the battery compartment is almost always visible once you open the main cover. The 9-volt battery connector is a distinctive rectangular plug with two metal terminals. You cannot miss it once the cover is off.

Open the alarm cover safely

First Alert alarms use one of two cover designs. The most common is a tab-release cover: look for a small plastic tab on the edge of the cover, usually on the side or bottom. Press this tab firmly and the cover will pop out or swing open. The second design is a twist-lock cover: grip the outer ring of the alarm and turn it counterclockwise about a quarter turn until the cover releases.

Do not force either type. If the cover does not move after gentle pressure, you may have the wrong model or the cover may be stuck from dust. Wipe the seam with a dry cloth and try again. Once the cover is open, you will see the battery connector when ready — it is a white or black plastic block with two metal prongs sticking out.

Remove the old battery and install the new one

Grip the old 9-volt battery by its sides and pull it straight out of the connector. The battery should come free with light pressure — do not twist or wiggle it excessively. Once it is out, check the connector for any corrosion (a white or green crusty buildup on the metal prongs). If you see corrosion, wipe the prongs clean with a dry cloth before inserting the new battery.

Slide the new 9-volt battery into the connector with the positive terminal (marked with a +) facing up or toward the connector, depending on your model. Push the battery straight in until you hear or feel a click. The battery should sit flush against the connector — if it sticks out or feels loose, remove it and reinsert it. A properly seated battery will not rattle or move when you gently shake the alarm.

Test the alarm and close the cover

Before closing the cover, press the large test button on the front of the alarm. The alarm should sound a loud chirp or beep within a few seconds. If it does not sound, the battery may not be seated correctly — remove it, check the connector for debris, and try again. Once the alarm sounds, you know the battery is working and the alarm is functioning.

Close the cover by reversing the opening step: push the tab-release cover back in until it clicks, or twist the cover clockwise until it locks. The cover should sit flush with the body of the alarm with no gaps. Your alarm is now ready to detect smoke.

When to replace the battery and what the warning sounds mean

Replace your smoke alarm battery once a year, ideally in the fall or spring when you change your clocks. Mark the date on the battery itself with a permanent marker so you know when you last changed it. Some people change their batteries on their birthday or on a holiday they remember easily.

If your alarm chirps every 30 to 40 seconds, the battery is low and needs replacement when ready — this chirp is a warning signal, not a malfunction. A continuous loud alarm means the unit is detecting smoke and you should evacuate. A single chirp when you press the test button is normal and means the alarm is working. If the alarm does not sound when you press the test button after installing a new battery, the unit itself may have failed and should be replaced.

Hardwired alarms with backup batteries

If your smoke alarm is hardwired to your home's electrical system, it will have a backup 9-volt battery that powers the alarm if the power goes out. The backup battery is replaced exactly the same way as a battery-only alarm — open the cover, remove the old battery, and slide in a new 9-volt battery. Changing the backup battery does not interrupt your home's power or disable the alarm.

Hardwired alarms usually have a small light on the front that glows green or red to show the power status. If the light goes out after you change the battery, the battery may not be seated correctly. Remove it and reinsert it. If the light still does not come on, the alarm may have lost its hardwired connection — check that the unit is screwed firmly to the ceiling or wall and that no wires have come loose inside the cover.

Frequently Asked Questions

What type of 9-volt battery should I buy?

Any standard 9-volt battery works in First Alert alarms — Duracell, Energizer, and store brands are all compatible. Alkaline batteries last longer than carbon-zinc batteries. Buy a pack of two or three so you have a spare on hand when the next replacement is due.

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

The battery may not be fully seated in the connector. Remove it and reinsert it firmly until you hear a click. If it still chirps, the battery itself may be defective — try a different new battery. If the alarm continues to chirp with a fresh battery, the unit may have reached the end of its life and should be replaced.

Can I use a rechargeable 9-volt battery?

Rechargeable 9-volt batteries work but are not recommended for smoke alarms because they lose charge faster than alkaline batteries and may not power the alarm during a power outage. Stick with standard alkaline 9-volt batteries for the most reliable protection.

Do I need to turn off power before changing a hardwired alarm battery?

No. The backup battery change does not require you to cut power to the alarm or your home. The alarm will continue to run on hardwired power while you swap the battery. You can change the battery at any time without affecting the alarm's operation.

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

A standard alkaline 9-volt battery lasts about one year in a smoke alarm that is not actively detecting smoke. If your alarm sounds frequently due to cooking smoke or steam, the battery may drain faster. Replace it annually regardless, or when ready if the low-battery chirp starts.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.