Replace the battery by opening the alarm cover, sliding out the old battery, and inserting a new one of the same type

Most First Alert smoke alarms use a 9-volt battery that slides into a clip inside the alarm. The whole job takes about two minutes. Turn off the alarm at your breaker or unplug it if it's hardwired, open the cover by twisting or unclipping it, remove the old battery, and slide a fresh 9-volt battery into the clip with the terminals facing the right direction. Close the cover and test the alarm by pressing the test button for three seconds—you should hear a loud chirp.

The exact steps depend on your alarm model, but First Alert makes the process straightforward on all of them. If your alarm is hardwired to your home's electrical system, it will have a backup battery; you only need to replace that backup battery, not disconnect the alarm itself. If it's battery-powered only, you do not need to turn anything off before you start.

Key Takeaways

  • First Alert smoke alarms typically use a 9-volt battery that slides into a clip inside the alarm cover.
  • The alarm will chirp every 30 to 60 seconds when the battery is low, which is your signal to replace it.
  • Always test the alarm after installing a new battery by pressing the test button for three seconds and listening for a loud chirp.
  • If your alarm is hardwired, you only replace the backup battery; the alarm stays connected to your home's power.
  • Buy a fresh 9-volt battery from a grocery store, pharmacy, or hardware store—old or expired batteries may not work reliably.

Locate the battery compartment and open the alarm cover

The battery compartment is inside the alarm cover. On most First Alert models, you open the cover by twisting it counterclockwise a quarter turn, or by pressing a clip on the side and pulling the cover away from the base. The cover is usually white or off-white plastic and sits flush against the round or rectangular base that is mounted to your ceiling or wall.

If you are not sure which direction to twist, try counterclockwise first—that is the standard for most First Alert alarms. If it does not budge, look for a small clip or tab on the edge of the cover. Press it gently and pull the cover straight down or toward you. Do not force it; the cover should come off with light pressure once you have found the right release point.

Remove the old battery and note its type

Once the cover is open, you will see the battery clip inside. The old battery slides into this clip horizontally or vertically depending on the model. Grip the battery by its sides (not the terminals) and pull it straight out of the clip. Set it aside—you do not need to recycle it when ready, but 9-volt batteries should go to a battery recycling program rather than the trash.

Look at the label on the old battery. It will say "9V" or "9 Volt." Write down the brand if you want to buy the same one again, but any standard 9-volt battery will work. Avoid very old batteries or ones that have been sitting in a drawer for years; they may have lost charge and will not power the alarm reliably.

Insert the new battery into the clip

Take your new 9-volt battery and look at the terminals on top—one is marked with a plus sign (+) and one with a minus sign (−). The clip inside your alarm has two metal contacts that match these terminals. Slide the battery into the clip so that the plus terminal touches the plus contact and the minus terminal touches the minus contact. You will hear or feel a small click when the battery seats fully in the clip.

If the battery does not slide in smoothly, stop and check the orientation. The terminals should line up with the contacts in the clip. Forcing a battery in the wrong direction can damage the clip or the battery. Once it is seated, the battery should not move when you gently tug on it.

Close the alarm cover and test the alarm

Replace the cover by reversing the motion you used to open it. If you twisted it counterclockwise to open, twist it clockwise to close. If you pressed a clip to open, align the cover with the base and push it on until you hear a click. The cover should sit flush against the base with no gaps.

Press and hold the test button on the front of the alarm for three seconds. The alarm should sound a loud, continuous chirp. If it does not sound, open the cover again and check that the battery is fully seated in the clip. If the battery is seated correctly and the alarm still does not sound, the battery may be defective—try a different new battery.

What to do if the alarm keeps chirping after battery replacement

A single chirp every 30 to 60 seconds after you have installed a new battery usually means the battery is not making good contact with the clip. Open the cover, remove the battery, and look at both the battery terminals and the metal contacts in the clip. If either is dirty or corroded, wipe them gently with a dry cloth or a pencil eraser. Reinsert the battery and test again.

If the alarm continues to chirp after you have cleaned the contacts, the clip itself may be damaged or the alarm may have reached the end of its life. First Alert smoke alarms typically last 8 to 10 years. If your alarm is older than that, replacing the entire unit is safer than continuing to troubleshoot a failing alarm.

Hardwired alarms with backup batteries

If your First Alert alarm is hardwired to your home's electrical system, it will have a backup battery inside. You do not need to turn off the power to your home or disconnect the alarm to replace this battery. straightforward open the cover and replace the backup battery the same way you would on a battery-powered alarm. The alarm will continue to draw power from your home's electrical system while you work.

Hardwired alarms with backup batteries are common in newer homes or homes with interconnected smoke detection systems. The backup battery ensures the alarm keeps working if the power goes out. Replace the backup battery as soon as you hear the low-battery chirp, just as you would on a battery-only alarm.

Frequently Asked Questions

What size battery does a First Alert smoke alarm use?

Most First Alert smoke alarms use a standard 9-volt battery. Check the label inside the alarm cover or the manual that came with your alarm to confirm. Some older or specialty models may use different sizes, but 9-volt is by far the most common.

How often do I need to replace the battery?

A 9-volt battery in a smoke alarm typically lasts six months to one year, depending on the brand and how often the alarm tests itself. Your alarm will chirp every 30 to 60 seconds when the battery is low, which is your signal to replace it. Do not ignore the chirp—a low battery means the alarm cannot protect you if there is a fire.

Can I use a rechargeable 9-volt battery?

Rechargeable 9-volt batteries are not recommended for smoke alarms. They tend to lose charge faster than standard alkaline batteries and may not provide reliable power in an emergency. Stick with a fresh alkaline 9-volt battery from a store.

What if the alarm still does not work after I replace the battery?

First, test the new battery in another device to make sure it is not defective. If the battery works elsewhere, open the alarm cover and check that the battery is fully seated in the clip and the terminals are clean. If the alarm still does not sound after testing, the alarm itself may be faulty and should be replaced.

Do I need to turn off power before replacing a hardwired alarm's backup battery?

No. Hardwired alarms remain powered by your home's electrical system while you replace the backup battery. You can open the cover and swap the battery without turning off any breakers or disconnecting the alarm.