Replace the battery in under two minutes
Most First Alert smoke detectors use a 9-volt battery that slides or twists out of the unit. Open the detector cover by pressing the tab or twisting the faceplate counterclockwise, remove the old battery, and insert a fresh 9-volt battery with the terminals facing the correct direction. Close the cover and press the test button to confirm the detector works. The whole job takes about 90 seconds.
First Alert makes several detector models, and the battery type and removal method vary slightly depending on which one you own. The most common residential models use a 9-volt battery, but some use AA or AAA batteries instead. Check the label on your detector or the manual to confirm which type yours needs before you buy a replacement.
Key Takeaways
- Most First Alert detectors use a 9-volt battery that you access by pressing a tab or twisting the faceplate open.
- Always test the detector after installing a new battery by pressing the test button until the alarm sounds.
- If the alarm does not sound after you install a fresh battery, the detector itself may have failed and needs replacement.
- Replace batteries once a year, or when ready when the detector beeps every 30 to 60 seconds to signal low battery.
Locate the battery compartment on your detector
The battery compartment is usually on the back or side of the detector faceplate. Look for a small tab labeled "battery" or a seam where the faceplate meets the base. Some models have a hinged cover that swings down; others have a faceplate that twists counterclockwise to open.
If you cannot find the compartment, check the manual or look up your specific model number on the First Alert website. The model number is printed on a label on the back of the detector. Knowing the exact model saves time and prevents you from forcing open a cover that twists rather than slides.
Remove the old battery and note the terminal positions
Once the compartment is open, you will see the battery holder with two metal terminals. The positive terminal (marked with a + sign) and negative terminal (marked with a − sign) must face a specific direction for the battery to work. Before you pull out the old battery, look at which way the terminals are oriented—or take a photo with your phone so you remember.
Slide or lift the old battery straight out. Do not force it; if it is stuck, wiggle it gently side to side. Dispose of the old battery according to your local recycling rules. Many retailers like Best Buy and Home Depot accept used 9-volt batteries for free recycling.
Install the new 9-volt battery
Hold the new battery so the positive terminal (the larger of the two metal connectors on top) faces the positive terminal in the holder. Slide the battery in smoothly until it sits flat in the compartment. You should hear or feel a small click when the battery makes contact with the terminals.
Do not force the battery in at an angle. If it does not slide easily, remove it and check that the terminals are aligned correctly. A battery installed backward will not make contact and the detector will not work.
Close the cover and test the detector
Swing the cover closed or twist the faceplate clockwise until it sits flush against the base. Press and hold the test button on the front of the detector for three to five seconds. You should hear a loud alarm sound—this confirms the battery is installed correctly and the detector is working.
If the alarm does not sound, open the cover and check that the battery terminals are making contact. Remove the battery, wait five seconds, and reinstall it. Test again. If the detector still does not alarm after a fresh battery and correct installation, the detector itself has likely failed and should be replaced.
When to replace the battery and what the low-battery beep sounds like
Replace the battery once per year, even if the detector has not beeped. Many fire safety experts recommend changing batteries when you change your clocks for daylight saving time—it is an straightforward reminder. Mark it on your calendar or set a phone reminder for the same date each year.
A low-battery warning sounds like a single short beep every 30 to 60 seconds. It is much quieter and shorter than the alarm that sounds when you press the test button. If you hear this pattern, replace the battery right away. The detector will continue to work for a short time after the low-battery beep starts, but the battery is nearly drained.
Hardwired detectors with battery backup
Some First Alert smoke detectors are hardwired into your home's electrical system but also have a backup battery. These detectors have a 9-volt battery compartment even though they are powered by house current. The battery only activates if the power goes out, so you may not realize it has died until a blackout occurs.
Replace the backup battery once per year using the same steps as above. If your hardwired detector beeps every 30 to 60 seconds, the backup battery is low—replace it even if the detector is receiving power from the wall. Some hardwired models also beep if the detector itself is failing; if the beeping continues after you install a fresh battery, call a licensed electrician to inspect the wiring or replace the unit.
Frequently Asked Questions
What size battery does my First Alert detector use?
Most First Alert residential smoke detectors use a 9-volt battery. Some models use two AA or AAA batteries instead. Check the label on the back of your detector or the manual to confirm. The model number on the label will help you find the correct battery type online if you are unsure.
Can I use a rechargeable battery in my smoke detector?
No. Smoke detectors require a fresh alkaline battery to work reliably. Rechargeable batteries lose charge over time even when not in use, and a low or dead battery in a smoke detector puts your home at risk. Always use a new alkaline 9-volt or AA/AAA battery.
Why does my detector keep beeping even after I put in a new battery?
If the beeping continues after you install a fresh battery and test the detector, the unit itself may have failed. Some detectors also beep if they detect dust or debris inside. Try gently vacuuming the vents with a soft brush attachment, then test again. If it still beeps, replace the entire detector.
How long does a smoke detector battery last?
A fresh alkaline 9-volt battery typically lasts six to 12 months in a smoke detector, depending on how often the detector tests itself and sounds alarms. Replace the battery once per year as a safety practice, or when ready when you hear the low-battery beep.
Do I need to turn off power before replacing a hardwired detector battery?
No. The battery compartment is isolated from the electrical wiring, so you can safely replace the backup battery while the detector is powered. However, if you are uncomfortable working near electrical components, a licensed electrician can replace the battery for you.