How to Change the Battery in a First Alert Smoke Detector

Open the detector and remove the old battery

Most First Alert smoke detectors have a battery compartment on the back or bottom of the unit. Look for a small latch or clip holding the compartment door closed. Press or slide this latch—the exact motion depends on your model—and the door will swing open or slide out. Inside you will see a 9-volt battery (shaped like a small rectangular block with two terminals on top) or two AA batteries, depending on which First Alert model you own.

Gently pull the battery straight out. If it is a 9-volt battery, grip it by the body, not the terminals. If it is AA batteries, slide them out of their holder. Set the old battery aside—you will need to dispose of it properly at a battery recycling center or hazardous waste collection site, not in the trash.

Key Takeaways

First Alert detectors use either one 9-volt battery or two AA batteries, depending on the model number printed on the back.
Open the battery compartment by pressing or sliding the latch on the back or bottom of the detector.
Insert the new battery in the same orientation as the old one—the positive and negative terminals must face the correct direction.
Close the compartment door and test the detector by pressing the test button for three seconds until you hear the alarm.
If the detector still chirps after a fresh battery, the unit itself may have reached the end of its life and needs replacement.

Insert the new battery in the correct direction

Before you insert the new battery, look at how the old one was positioned. The terminals or contact points must face the same direction. On a 9-volt battery, the two metal terminals on top connect to the springs or contacts inside the compartment. On AA batteries, the flat end (negative) and the bumped end (positive) align with the metal contacts in the holder.

Slide or insert the new battery slowly until it sits flat in the compartment. You should feel it settle into place. Do not force it—if it does not slide in smoothly, you may have the polarity reversed. Remove it, flip it around, and try again.

Close the compartment and test the detector

Push the battery compartment door closed until you hear or feel it latch. The door should sit flush with the body of the detector with no gaps. If it does not close all the way, the battery may not be seated correctly—open it again and check the position.

Now test the detector. Locate the test button on the front or side of the unit—it is usually labeled "TEST" in white or red lettering. Press and hold this button for three seconds. You should hear a loud alarm sound. If you hear nothing, open the compartment again and verify the battery is making contact with the terminals. If the detector still does not sound, the unit may have reached the end of its service life and will need to be replaced.

Know when your First Alert detector needs a new battery

Most First Alert smoke detectors will chirp or beep 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 continuous wail. When you hear this chirp, it is time to change the battery, even if the detector still sounds the alarm when you press the test button.

If you change the battery and the chirping continues, the battery compartment contacts may be corroded or dirty. Open the compartment again and look at the metal contacts. If they appear dark or discolored, wipe them gently with a dry cloth or a pencil eraser to remove any buildup. Reinsert the battery and test again.

Replace the entire detector if it is past its expiration date

Every First Alert smoke detector has a manufacturing date printed on the back or bottom of the unit. Look for a label that says "Manufactured" followed by a date. Most smoke detectors are designed to last 8 to 10 years from the date of manufacture. If your detector is older than this, changing the battery will not restore it to full function—the internal sensors degrade over time and become less reliable.

If your detector is past its expiration date, purchase a new one rather than continuing to rely on the old unit. A detector that is 10 years old may fail to alarm in a real fire, even with a fresh battery. Write the installation date on the new detector with a permanent marker so you know when to replace it again.

Dispose of the old battery safely

9-volt and AA batteries contain materials that can harm the environment if they end up in a landfill. Do not throw them in the trash. Instead, take them to a battery recycling program. Many retailers that sell batteries—including Best Buy, Home Depot, and Lowe's—accept used batteries for free recycling at their customer service desk.

You can also search for a local hazardous waste collection site by visiting Earth911.com or calling your city or county waste management office. Some communities hold special collection days for batteries and other hazardous household items. Storing old batteries in a cool, dry place until you can recycle them is safe and keeps them out of the waste stream.

Frequently Asked Questions

How often should I change the battery in my First Alert smoke detector?

Change the battery once a year as part of routine maintenance, or when ready when you hear the low-battery chirp. Many people change their smoke detector batteries when they change their clocks for daylight saving time, which makes it straightforward to remember. If you hear chirping, do not wait for your scheduled maintenance date—install a fresh battery right away.

What if my First Alert detector uses AA batteries instead of a 9-volt?

The process is identical. Open the compartment, remove both old AA batteries, and insert two new AA batteries in the same orientation. Make sure both batteries are fresh—if one is old and one is new, the detector may not function properly. Test the detector after installation to confirm the alarm sounds.

Can I use a rechargeable battery in my First Alert smoke detector?

No. First Alert detectors are designed for single-use alkaline batteries only. Rechargeable batteries have different voltage output and may not power the detector reliably. Always use new alkaline 9-volt or AA batteries from a reputable manufacturer.

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

The battery may not be making full contact with the terminals. Open the compartment and check that the battery is seated all the way in. If the contacts look dirty or corroded, wipe them with a dry cloth. If chirping continues after reinsertion, the detector itself may be faulty and need replacement.

Is it safe to leave a smoke detector without a battery while I am buying a new one?

No. A detector without a battery cannot sound an alarm in a fire. If you remove the old battery, install the new one when ready—do not leave the detector unpowered, even for a few hours. If you do not have a replacement battery on hand, purchase one before you remove the old one.

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.