Replace the battery in under two minutes

Most First Alert smoke alarms use a 9-volt battery that slides out of the back or bottom of the unit. Turn off the alarm's power switch if it has one, then press the release tab or button on the alarm body—usually marked with an arrow—and the battery compartment will pop open or slide out. Remove the old battery, note which direction the terminals face (the red and black wires), and slide the new 9-volt battery in the same way. Close the compartment, and the alarm is ready to work again.

The whole job takes about 90 seconds. First Alert alarms are designed so you do not need tools, and the battery compartment is always accessible from outside the unit without removing it from the ceiling or wall.

Key Takeaways

  • First Alert smoke alarms use a standard 9-volt battery that you can buy at any drugstore, grocery store, or hardware retailer for $5 to $10.
  • The battery compartment opens by pressing a release tab or button on the alarm body—no screwdriver or disassembly required.
  • Pay attention to which way the battery terminals face when you remove the old one, so you insert the new battery the same way.
  • Test the alarm when ready after replacing the battery by pressing the test button on the alarm body; you should hear a loud chirp or alarm sound.
  • Replace the battery once a year, or sooner if the alarm chirps every 30 to 40 seconds (the low-battery warning).

Locate the battery compartment on your alarm

First Alert makes several models, but the battery compartment is always on the outside of the unit. On ceiling-mounted alarms, the compartment is usually on the bottom or back edge. On wall-mounted alarms, it is typically on the side or bottom. Look for a small rectangular door or a button labeled "BATT" or with a battery icon.

If you cannot find the compartment, check the user manual that came with the alarm—you can also search "First Alert [your model number] manual" online and read a PDF. The model number is printed on the back or bottom of the alarm body.

Open the compartment and remove the old battery

Press the release tab or button firmly. You may hear a small click. The compartment door will either pop open or slide out toward you. Do not force it; if it does not move, you are pressing the wrong button.

Once the compartment is open, you will see the 9-volt battery connected to two wires—one red, one black. Note which wire is connected to which terminal on the battery (the red wire goes to the positive terminal, the black to the negative). Gently pull the battery straight out of the connector. If the connector is tight, wiggle the battery slightly side to side as you pull, but do not yank hard enough to damage the wires.

Insert the new battery and close the compartment

Take a fresh 9-volt battery and align it so the red wire connects to the positive terminal (marked with a +) and the black wire to the negative terminal (marked with a −). Push the battery firmly into the connector until you hear or feel a click. The battery should sit flush in the compartment with no gaps.

Slide the compartment door closed or press it shut until it clicks. You should hear a small snap. If the alarm beeps or chirps once, that is normal—it means power has been restored. Do not worry if it does not beep; some models are silent when the battery is installed.

Test the alarm to confirm it is working

Press and hold the test button on the alarm body for three to five seconds. The button is usually in the center of the alarm face and may be labeled "TEST." You should hear a loud alarm sound—either a steady tone or a pulsing chirp, depending on your model. If you hear nothing, the battery may not be fully seated in the connector, or the connector itself may be damaged.

If the alarm does not sound, remove the battery, wait 10 seconds, and reinsert it, making sure the wires are connected firmly. Test again. If it still does not work, the alarm may need replacement rather than just a new battery.

Common mistakes to avoid

The most common error is installing the battery backward—red wire to negative, black to positive. This will not damage the alarm, but it will not work. If the alarm is silent after you close the compartment, open it again and check the wire connections.

Another mistake is using the wrong battery size. First Alert smoke alarms use 9-volt batteries, not AA, AAA, or any other size. If you buy the wrong size by accident, it will not fit in the compartment. A standard 9-volt battery is rectangular and about the size of a lighter.

Do not leave the compartment door open or partially closed. This can allow dust into the alarm and may prevent the battery from making a solid connection. Always close it fully until you hear the click.

When to replace the battery

Replace the battery once a year, ideally in the spring or fall when you change your clocks. Mark it on your calendar so you do not forget. Many people replace batteries on their birthday or on the first day of a season.

If your alarm chirps every 30 to 40 seconds, the battery is low and needs replacement when ready, even if you just installed a new one a few months ago. This chirp is the alarm's low-battery warning and will continue until you replace the battery. A low battery does not mean the alarm is broken—it just means the battery has lost its charge and cannot power the smoke detector.

Frequently Asked Questions

Can I use a rechargeable 9-volt battery in my First Alert smoke alarm?

Rechargeable 9-volt batteries work in First Alert alarms, but they drain faster than standard alkaline batteries and may not power the alarm long enough to meet safety standards. Stick with a fresh alkaline 9-volt battery from a store. They cost $5 to $10 and last a full year.

What if the battery connector is loose or damaged?

If the wires are loose but still attached, you may be able to gently push the connector back onto the battery terminal. If the wires are cracked, frayed, or the connector is broken, the alarm cannot be safely repaired and should be replaced. Do not try to tape or solder the wires yourself.

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

The alarm may still be detecting a low battery if the new battery is defective or if the old battery was not fully removed. Remove the new battery, wait 30 seconds, and reinsert it firmly. If it still chirps, try a different new battery from a different package or store. If a brand-new battery does not stop the chirping, the alarm itself may be faulty.

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

If your alarm has a power switch, turn it off before opening the battery compartment. This is a safety precaution and only takes a second. If there is no switch, you do not need to do anything—just open the compartment and swap the battery.

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

A standard alkaline 9-volt battery lasts about one year in a First Alert smoke alarm. The exact time depends on how often the alarm tests itself and whether it has ever been triggered. Replace it once a year to be safe, or sooner if you hear the low-battery chirp.