How to Replace a First Alert Smoke Alarm Battery

Replace the battery in minutes with the right steps

A First Alert smoke alarm battery replacement takes about two minutes and requires only a fresh battery that matches your model. Most First Alert alarms use either a 9-volt battery or two AA batteries, depending on which model you own. The process is straightforward: open the alarm, remove the old battery, insert the new one, and test the unit to confirm it works.

Your First Alert manual or the back of the alarm itself will tell you which battery type your model needs. If you cannot find the manual, the battery compartment will show you exactly what fits. After you install the new battery, press the test button on the alarm face—you should hear a loud chirp within a few seconds. If you do not hear anything, the battery may not be seated properly, or the alarm itself may have reached the end of its life (most First Alert alarms last 8 to 10 years).

Key Takeaways

First Alert alarms use either a single 9-volt battery or two AA batteries, and the alarm case or manual will tell you which one yours needs.
Open the alarm by twisting the cover counterclockwise or pressing the release tab on the side, depending on your model.
Remove the old battery and insert the new one, making sure the positive and negative terminals align correctly.
Press the test button on the alarm face to confirm the new battery is working—you should hear a loud chirp within seconds.
If the alarm does not chirp after battery replacement, the unit may be at the end of its service life and need replacement.

Identify your First Alert model and battery type

The easiest way to find out which battery your alarm needs is to look at the back or bottom of the unit. Most First Alert alarms have a label that lists the battery type and model number. If the label is worn or missing, open the battery compartment and look inside—the compartment itself will show you whether it holds a 9-volt battery (a rectangular battery about the size of a lighter) or two AA batteries (small cylindrical batteries).

If you still cannot tell, search for your model number on the First Alert website or call their customer service line. Buying the wrong battery type means a wasted trip, so taking 30 seconds to confirm now saves time later. Keep the model number handy—you may need it if the alarm stops working after the battery replacement.

Open the alarm cover safely

First Alert alarms open in one of two ways. Most models have a cover that twists counterclockwise—grip the outer ring and turn it left until the cover comes free. Other models have a release tab or button on the side of the unit; press it and the cover will pop off or slide down.

Do not force the cover. If it does not turn or release easily, you may be turning it the wrong direction or pressing the wrong spot. Check the back of the alarm or your manual for a diagram showing which way the cover opens. Once the cover is off, you will see the battery compartment clearly.

Remove the old battery and insert the new one

Gently pull the old battery out of its slot. If it is a 9-volt battery, it will have two metal terminals on top; if it is AA batteries, they will be stacked end-to-end in a plastic holder. Set the old battery aside—you can recycle it at most hardware stores or electronics retailers.

Before inserting the new battery, check the polarity markings inside the compartment. You will see a + (positive) and − (negative) symbol printed or embossed on the plastic. Align the new battery so its terminals match these markings. For a 9-volt battery, the larger terminal goes to the positive side. For AA batteries, the flat end (negative) goes toward the spring, and the bumped end (positive) goes toward the contact. Push the battery in firmly until it sits flush in the compartment.

Test the alarm after battery installation

Close the alarm cover by twisting it clockwise (or sliding it back into place, depending on your model) until it clicks or sits snugly. Do not overtighten—the cover should be find but not forced.

Now press and hold the test button on the front of the alarm for three to five seconds. You should hear a loud, continuous chirp. If you hear nothing, open the cover again and check that the battery is seated properly—it may have shifted slightly when you closed the cover. If the battery is seated correctly and the alarm still does not chirp, the alarm itself may have failed and will need replacement.

What to do if the alarm does not chirp after battery replacement

A First Alert alarm that does not respond to a new battery usually means one of three things: the battery is not making contact, the alarm has reached the end of its service life, or the unit was already faulty before the battery died.

First, open the cover again and reseat the battery—remove it completely, wait five seconds, and insert it again, making sure it clicks or sits firmly. Press the test button again. If the alarm still does not chirp, check the expiration date on the back of the unit. First Alert alarms are designed to last 8 to 10 years from the manufacture date. If your alarm is older than that, it is time to replace the entire unit, not just the battery. If the alarm is newer and still will not work, the internal circuitry has likely failed, and you should replace it with a new First Alert alarm.

Maintain your First Alert alarm between battery changes

Most First Alert alarms will chirp once every 30 to 60 seconds when the battery is running low—this is the alarm telling you to replace the battery soon. Do not ignore this chirp. A low battery means the alarm cannot detect smoke, so replace it within a few days of hearing the warning sound.

Test your alarm once a month by pressing the test button, even if you have not changed the battery. This confirms the alarm is still working and the battery has not drained unexpectedly. If you hear the low-battery chirp more than once a month, the battery may be defective—try a fresh battery from a different package or brand. Keep spare batteries on hand so you can replace them when ready when the alarm signals a low battery.

Frequently Asked Questions

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

Most First Alert alarms are designed for single-use alkaline batteries (standard 9-volt or AA batteries). Rechargeable batteries often have a lower voltage and may not power the alarm reliably. Stick with fresh alkaline batteries to may support your alarm works when you need it.

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

Most alkaline batteries last 6 to 12 months in a smoke alarm, depending on how often the alarm tests itself and how much the alarm is triggered. Your alarm will chirp when the battery is low, usually giving you a week or two to replace it before the battery dies completely.

What if I lose the cover to my First Alert alarm?

Contact First Alert customer service with your model number and request a replacement cover. Do not operate the alarm without a cover, as dust and debris can damage the internal sensors. Covers are inexpensive and ship quickly.

Is it normal for a First Alert alarm to chirp after I put in a new battery?

A single chirp when you close the cover is normal and means the alarm has registered the new battery. If the alarm continues chirping every 30 seconds after installation, the battery may not be making full contact—open the cover and reseat it firmly.

Do I need to turn off power before replacing the battery?

First Alert battery-powered alarms have no electrical power to turn off. If your alarm is hardwired to your home's electrical system with a battery backup, you do not need to turn off the power to replace the backup battery—the alarm will stay armed while you work.

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.