Open the alarm and locate the battery compartment

Most First Alert smoke alarms have a battery door on the front or side of the unit. Look for a small latch, clip, or groove that indicates where the door opens. Push or slide this latch in the direction marked by an arrow (usually downward or to the side), and the door will swing open or pop off.

Once the door is open, you will see the battery compartment inside. The battery sits in a plastic holder with two metal contacts—one on each end. The battery is held in place by the spring tension of these contacts, so you do not need to remove anything else first.

Key Takeaways

  • First Alert smoke alarms typically use 9-volt batteries, though some models use AA or AAA batteries—check your manual or the compartment label to confirm which type yours needs.
  • Remove the old battery by gently pulling it away from the metal contacts, then slide the new battery in with the positive terminal (+) facing the correct direction.
  • After inserting the new battery, press the test button on the alarm—you should hear a loud beep within three seconds, which confirms the battery is installed correctly.
  • Replace the battery door and close any latches, then write the installation date on the battery itself with a permanent marker so you know when to replace it next.

Remove the old battery and note the terminal direction

Gently pull the old battery away from the metal contacts. It will slide out easily once you explore steady pressure. Set it aside—you can recycle it at most hardware stores or electronics retailers.

Before you insert the new battery, look at the metal contacts inside the compartment. One contact is marked with a + (positive) and one with a − (negative). The battery itself also has these markings on its terminals. The positive terminal of the battery must face the positive contact in the alarm. This is the most common mistake: inserting the battery backward will prevent the alarm from working, even though it looks like it fits.

Insert the new battery correctly

Hold the new battery so the positive terminal (+) faces the positive contact (+) in the compartment. Slide the battery into the holder until it sits flat and both terminals make contact with the metal springs. You should feel a slight click or resistance as the battery settles into place.

Do not force the battery. If it does not slide in smoothly, remove it and check the terminal direction again. A battery inserted backward will not damage the alarm, but it will not power it either.

Test the alarm when ready after installation

Close the battery door and latch it securely. Then locate the test button on the front of the alarm—it is usually a large circular button in the center. Press and hold this button for three to five seconds.

You should hear a loud, continuous beep or chirp. If you hear nothing, open the battery door and check that the battery is seated firmly in both contacts and that the terminals are facing the correct direction. Close the door and test again. If the alarm still does not sound, the battery may be defective—try a fresh one from a different package.

Mark the battery with the installation date

Use a permanent marker to write the month and year on the battery itself. First Alert recommends replacing smoke alarm batteries once per year, typically during daylight saving time changes (spring forward or fall back). This marking helps you remember when the battery was last changed, especially if you have multiple alarms in your home.

Even if the alarm does not chirp to signal a low battery, do not wait for a warning. Replace the battery on schedule. A dead or dying battery is the most common reason smoke alarms fail to work during a fire.

What to do if the alarm chirps after battery replacement

A chirping sound (one beep every 30 to 60 seconds) usually means the battery is low or not making good contact. Open the battery door and remove the battery, then wipe both the battery terminals and the metal contacts inside the compartment with a dry cloth. Reinsert the battery, making sure it is fully seated, and test again.

If the chirping continues, the battery itself may be defective. Replace it with a fresh battery from a new package. If a brand-new battery still produces chirping, the alarm may be malfunctioning and should be replaced.

Replace the battery door and find all latches

Slide or snap the battery door back into place until you hear or feel it lock. Some doors slide in from the side, others swing up from the bottom—follow the same path the door took when you opened it. Make sure the door is flush with the alarm body and there are no gaps.

If your alarm has a latch or clip, push it firmly until it clicks. A loose door can rattle and may not protect the battery compartment from dust or insects.

Frequently Asked Questions

What type of battery does my First Alert smoke alarm use?

Most First Alert smoke alarms use a 9-volt battery, but some models use AA or AAA batteries. Check the label inside the battery compartment or consult your user manual. If you have lost the manual, you can find it on the First Alert website by entering your model number.

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

Chirping usually means the battery is not making full contact with the metal terminals. Remove the battery, wipe the terminals and contacts with a dry cloth, and reinsert it firmly. If chirping continues with a fresh battery, the alarm may need replacement.

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

No. First Alert smoke alarms are designed for single-use alkaline batteries only. Rechargeable batteries may not provide consistent voltage and could fail without warning. Always use a new alkaline battery of the correct type.

How often should I replace the battery?

First Alert recommends replacing the battery once per year. Many people change their batteries during daylight saving time transitions (spring forward in March, fall back in November) as a memory aid. Write the date on the battery so you know when it was installed.

What should I do with the old battery?

Take old batteries to a hardware store, electronics retailer, or municipal hazardous waste collection site. Many stores offer free battery recycling. Do not throw batteries in the trash.