Replace the battery by opening the alarm cover, sliding out the old battery, and inserting a new one in the same direction
Most First Alert smoke alarms use a 9-volt battery held in a plastic clip inside the alarm body. To replace it, twist or slide the alarm cover off the mounting bracket on your ceiling or wall, locate the battery clip, press the clip to release the old battery, and slide a fresh 9-volt battery in with the positive terminal facing the correct direction. The whole job takes less than a minute.
First Alert alarms come in two main types: ionization alarms (which detect fast-flaming fires) and photoelectric alarms (which detect smoldering fires). Both use the same battery replacement method. Some dual-sensor models combine both types in one unit. Regardless of which type you own, the battery sits in the same spot and comes out the same way.
Key Takeaways
- Turn off the alarm before replacing the battery to avoid a false alarm or the alarm chirping during the swap.
- Use a fresh 9-volt battery; do not reuse an old one or mix battery brands in the same alarm.
- Insert the battery with the positive terminal facing up or toward the clip, depending on your model — check the label inside the alarm cover.
- Test the alarm after installation by pressing the test button for three seconds; the alarm should sound loudly.
- Replace batteries once a year, or whenever the alarm chirps to signal low battery.
Step-by-step battery replacement
Start by locating your First Alert alarm on the ceiling or wall. If it is currently alarming or chirping, press the test button on the front to silence it, or turn off power at the breaker if it is a hardwired model with battery backup.
Grip the alarm body and twist it counterclockwise (or slide it sideways, depending on your mounting bracket style) until it separates from the bracket. The bracket stays on the wall; only the alarm body comes down. Look inside the alarm cover for a plastic battery clip holding a 9-volt battery.
Press the clip or squeeze the sides of the clip to release the old battery. The battery will slide out. Note the direction the positive terminal was facing — this matters for the new battery. Slide a fresh 9-volt battery into the clip with the positive terminal facing the same direction as the old one. The clip will hold it snugly.
Twist or slide the alarm body back onto the bracket until it clicks or seats fully. Press the test button on the front for three seconds. The alarm should sound a loud chirp or beep. If it does not sound, the battery may be inserted backward — remove it and flip it around.
When to replace the battery
Replace the battery once per year, ideally on the same date each year so you remember. Many people change batteries when they set their clocks forward or back for daylight saving time. This keeps the alarm ready year-round.
If your alarm chirps once every 30 to 60 seconds, the battery is low and needs replacement when ready. This chirp is the alarm's way of signaling that the battery voltage has dropped below the level needed to detect smoke. Do not ignore this chirp — a low battery means the alarm cannot protect you.
Some First Alert models have a low-battery indicator light that blinks red instead of chirping. Check your manual to see which signal your model uses. Either way, replace the battery as soon as you hear or see the warning.
Choosing the right 9-volt battery
Buy a standard 9-volt battery from any grocery store, pharmacy, hardware store, or online retailer. Common brands include Duracell, Energizer, and Panasonic. All standard 9-volt batteries fit First Alert alarms — the connector is the same across brands.
Alkaline 9-volt batteries last about one year in a smoke alarm. Lithium 9-volt batteries cost more but last longer — up to 10 years in some models. Check your alarm's manual to see if it supports lithium batteries; most do, but a few older models do not.
Do not use rechargeable 9-volt batteries in smoke alarms. Rechargeable batteries have a lower voltage output and may not trigger the alarm reliably when smoke is present. Stick with single-use alkaline or lithium batteries.
Testing after battery replacement
After you insert the new battery and reattach the alarm, press and hold the test button on the front of the alarm for three seconds. The alarm should produce a loud, continuous sound — usually a beeping or chirping noise. If you hear nothing, the battery is likely inserted backward.
Remove the alarm from the bracket again, take out the battery, and flip it 180 degrees so the positive terminal faces the opposite direction. Reinsert the battery, reattach the alarm, and test again. The alarm should sound this time.
If the alarm still does not sound after flipping the battery, the battery itself may be dead or defective. Try a different new battery. If a second battery also fails to make the alarm sound, the alarm unit itself may have failed and need replacement.
Hardwired alarms with battery backup
Some First Alert smoke alarms are hardwired to your home's electrical system but also contain a 9-volt battery as backup power. If the power goes out, the battery keeps the alarm working. These alarms replace their batteries the same way as battery-only models.
If your hardwired alarm is chirping, it may be signaling low battery rather than a power problem. Replace the battery first. If the chirping continues after battery replacement, the alarm may be detecting a wiring issue — consult your manual or contact First Alert support.
Hardwired alarms should be tested monthly by pressing the test button. If the test button does not produce sound, replace the battery. If sound still does not come, turn off power at the breaker and check that the alarm is fully seated in its socket.
Common mistakes to avoid
Do not leave the alarm off the bracket while you replace the battery. Dust and insects can enter the alarm chamber and interfere with smoke detection. Keep the replacement process quick — remove the old battery, insert the new one, and reattach the alarm within a minute or two.
Do not mix old and new batteries in the same alarm, and do not use batteries from different brands in a multi-alarm setup. Mixing can cause one alarm to drain faster than others, leaving some unprotected.
Do not assume the alarm is working just because it looks clean. Always press the test button after replacing the battery. A silent alarm is worse than no alarm — you will not know it has failed.
Frequently Asked Questions
Why does my First Alert alarm keep chirping even after I replace the battery?
A continuing chirp usually means the battery is still low or inserted backward. Remove the alarm, flip the battery 180 degrees, and retest. If chirping continues, try a brand-new battery from a fresh package — the battery you installed may have been defective. If a second new battery also chirps, the alarm itself may have reached the end of its life and need replacement.
Can I use a different size battery, like an AA or AAA?
No. First Alert smoke alarms are designed for 9-volt batteries only. The connector and voltage requirements are specific to 9-volt cells. Using a different size will not fit, and even if you tried to adapt it, the alarm would not function correctly.
How long does a 9-volt battery last in a smoke alarm?
An alkaline 9-volt battery typically lasts about one year in a smoke alarm. Lithium 9-volt batteries can last up to 10 years. The exact lifespan depends on how often the alarm tests itself and whether it has detected any smoke. Replace batteries annually regardless of how long they claim to last.
What should I do with the old battery after I remove it?
Take used 9-volt batteries to a battery recycling program. Many retailers like Best Buy and Home Depot accept used batteries for free recycling. Do not throw them in the trash — batteries contain materials that should be recovered and reused.
Do I need to turn off power before replacing a battery in a hardwired alarm?
No. Turning off power is not necessary for battery replacement alone. The alarm will continue to run on AC power while you swap the battery. However, if you are working on the wiring or mounting bracket, turn off power at the breaker for safety.