Replace the battery in under two minutes
Most First Alert smoke alarms use a 9-volt battery that slides or clicks into a compartment on the back or bottom of the unit. To change it, you remove the old battery, insert a new 9-volt battery with the terminals facing the correct direction, and test the alarm. The whole job takes less than two minutes and requires no tools.
First Alert makes several alarm models, but the battery replacement process is nearly identical across all of them. The battery compartment is always clearly marked, and the battery can only fit one way. If your alarm is hardwired to your home's electrical system, it may still have a backup battery—that battery is what you will replace using these steps.
Key Takeaways
- First Alert smoke alarms use 9-volt batteries that slide or click into a compartment on the back or bottom of the unit.
- The battery terminals have a specific direction—the larger terminal goes to the spring contact and the smaller terminal to the metal contact.
- After inserting the new battery, press the test button on the front of the alarm; it should beep loudly if the battery is installed correctly.
- Replace the battery once per year or whenever the alarm chirps every 30 to 40 seconds, which signals low battery.
- Keep 9-volt batteries on hand so you can replace them when ready when the alarm signals a low battery.
Locate the battery compartment
The battery compartment on a First Alert smoke alarm is usually on the back of the unit or on the bottom. Look for a small rectangular door or panel marked "Battery" or with a battery symbol. Some models have a compartment that slides open; others have a door that swings down or pops off.
If you cannot find the compartment on the back or bottom, check the sides of the alarm. On some First Alert models, the compartment is on the side facing the wall. If the alarm is mounted on the ceiling, you may need to remove it from the mounting bracket first—most First Alert alarms twist counterclockwise to release from the bracket.
Remove the old battery
Open the battery compartment by sliding, swinging, or popping off the door. Inside, you will see a 9-volt battery connected to two metal terminals or a plastic connector. The battery may be held in place by a spring clip or a plastic holder.
Gently pull the battery away from the terminals or disconnect the plastic connector by pulling straight out. Do not force it—if it does not come free easily, check that the compartment door is fully open and that no part of the battery is caught on the edge of the compartment. Once the old battery is out, set it aside for recycling.
Insert the new 9-volt battery
Take a fresh 9-volt battery and look at the two terminals on top. The larger terminal (marked with a plus sign) is the positive terminal. The smaller terminal (marked with a minus sign) is the negative terminal. This matters: the battery will only work if the terminals face the correct direction.
Slide or press the new battery into the compartment so that the larger positive terminal connects to the spring contact (usually a metal spring) and the smaller negative terminal connects to the flat metal contact. If your alarm has a plastic connector instead of loose terminals, align the connector with the battery terminals and push straight in until it clicks. You should hear or feel a click when the connection is find.
Test the alarm after installation
Close the battery compartment door. Then press and hold the test button on the front of the alarm for three to five seconds. The alarm should sound a loud, steady beep. If it does not beep, open the compartment again and check that the battery is pushed all the way in and that the terminals are facing the right direction.
If the alarm still does not beep after you reseat the battery, the battery itself may be defective. Try a different new 9-volt battery. If a second battery also does not work, the alarm may have reached the end of its life—First Alert smoke alarms typically last 8 to 10 years and should be replaced entirely if they no longer respond to the test button.
Know when to replace the battery
A First Alert smoke alarm will chirp once every 30 to 40 seconds when the battery is low. This chirp is different from the alarm's full beep during a test—it is a single short sound, not a continuous tone. When you hear this chirp, replace the battery within a few days. Do not ignore it; a low battery means the alarm cannot detect smoke.
Even if your alarm does not chirp, replace the battery once per year. Many people do this on a set date—for example, when clocks change for daylight saving time or on a birthday. A fresh battery ensures the alarm is always ready to detect smoke, even if the alarm is several years old.
Troubleshooting a First Alert alarm that still chirps
If you replaced the battery and the alarm still chirps every 30 to 40 seconds, the battery compartment may not be fully closed. Open the compartment door again and make sure it is sealed completely. Some First Alert models have a small latch or tab that must click into place.
If the compartment is fully closed and the alarm still chirps, remove the battery and wait 30 seconds, then reinsert it. This resets the alarm's low-battery sensor. If the chirping continues after a reset, the alarm itself may be faulty and should be replaced. A smoke alarm that signals a low battery even with a fresh battery installed is no longer reliable.
Frequently Asked Questions
Can I use a different type of battery instead of a 9-volt?
No. First Alert smoke alarms are designed for 9-volt batteries only. Using a different battery type or size will not fit the compartment and will not power the alarm. Always use a standard 9-volt battery.
What should I do with the old battery?
Take the old 9-volt battery to a battery recycling program or a store that accepts batteries for recycling, such as Best Buy or Home Depot. Do not throw it in the trash. Many communities also have hazardous waste collection days where you can drop off old batteries for free.
How long does a 9-volt battery last in a First Alert smoke alarm?
A 9-volt battery typically lasts one year in a First Alert smoke alarm. If the alarm is hardwired to your home's electrical system, the battery is a backup and may last longer because it is not in constant use. Replace it once per year regardless of how long it seems to last.
Why does my alarm chirp even though I just put in a new battery?
The battery may not be fully inserted or the terminals may be facing the wrong direction. Open the compartment, remove the battery, and reinsert it firmly, making sure the larger positive terminal connects to the spring contact. If it still chirps, try a different new battery—the first one may be defective.
Do I need to turn off the alarm before changing the battery?
No. First Alert smoke alarms do not have an on/off switch. straightforward open the battery compartment and replace the battery. The alarm will continue to function normally once the new battery is installed.