Replace the battery in most First Alert models by opening the detector cover, sliding out the old battery, and inserting a new one of the same type

First Alert smoke detectors use one of two battery types depending on the model: either a 9-volt rectangular battery or two AA batteries. The process takes less than a minute. Open the detector cover (usually by twisting counterclockwise or unclipping a latch), note which battery type is inside, remove the old battery, and slide in a fresh one with the terminals facing the correct direction. Your detector will chirp once to confirm the battery is seated properly.

Most First Alert models chirp every 30 to 60 seconds when the battery is low—this is the signal to replace it. Do not ignore these chirps. A detector with a dead battery cannot alert you to smoke or fire.

Key Takeaways

  • First Alert detectors use either 9-volt or AA batteries depending on the model; check your detector or manual to know which type to buy.
  • Open the cover by twisting counterclockwise or unclipping the side latch, then slide the old battery out and the new one in.
  • The detector will chirp once when the new battery is seated correctly; if it does not chirp, remove and reinsert the battery to may support proper contact.
  • Replace batteries once a year as part of routine maintenance, even if the detector is not chirping yet.
  • If the detector continues to chirp after you install a new battery, the unit itself may have failed and should be replaced.

Finding the right battery type for your model

First Alert makes dozens of models, and not all use the same battery. The easiest way to find out which type yours needs is to open the detector and look inside. If you see a single rectangular battery about the size of a lighter, it takes a 9-volt. If you see two cylindrical batteries stacked or side by side, it takes AA batteries.

You can also check the back or side of the detector for a model number, then search "First Alert [model number] battery" online, or look at your original packaging or manual if you still have it. When you buy replacement batteries, buy alkaline (not rechargeable) batteries—they last longer in smoke detectors.

Step-by-step battery replacement

Step 1: Locate the cover latch. Most First Alert detectors have either a twist-off cover or a clip on the side. If it twists, hold the detector body steady with one hand and turn the cover counterclockwise with the other until it comes free. If it has a clip, look for a small lever or tab on the side of the detector and press or slide it to release the cover.

Step 2: Remove the old battery. Once the cover is open, you will see the battery or batteries inside. Slide the old battery out gently. If there are two AA batteries, remove both. Do not force them—they should slide out with light pressure.

Step 3: Insert the new battery. Slide the new battery in the same direction the old one came out. For 9-volt batteries, the terminals (the metal bumps on top) should face outward toward the detector's contacts. For AA batteries, check the + and − symbols inside the detector to orient them correctly. Push gently until the battery sits flush.

Step 4: Close the cover. Twist the cover clockwise until it clicks, or snap the clip back into place. The detector should chirp once. If it does not, open the cover again, remove the battery, and reinsert it to may support good contact.

What to do if the detector keeps chirping after battery replacement

If you install a fresh battery and the detector continues to chirp every 30 to 60 seconds, the detector itself has likely reached the end of its life. Most First Alert smoke detectors last 8 to 10 years. Even if the battery is new, a detector older than that should be replaced.

Remove the old detector from its mounting bracket (usually by twisting counterclockwise), disconnect any wires if it is hardwired, and install a new one in its place. Write the installation date on the new detector with a permanent marker so you know when to replace it.

Hardwired detectors with battery backup

Some First Alert models are hardwired into your home's electrical system but also have a backup battery. If your detector is mounted on the ceiling and has wires running into it, it is hardwired. The battery replacement process is the same—open the cover and swap the battery—but the detector will not stop working even if the battery is dead, because it draws power from your home's wiring.

The backup battery is there to keep the detector working during a power outage. Replace it once a year even if it is not chirping, because you will not know it has failed until the power goes out. If a hardwired detector chirps, replace the battery first; if it keeps chirping, the problem may be with the wiring or the detector itself, and you should call an electrician.

Battery maintenance and replacement schedule

Replace batteries in all your smoke detectors at the same time once a year. Many people do this when they change their clocks for daylight saving time in the spring, or on a birthday or holiday they will remember. This way you do not have to track which detector was replaced when.

Keep spare 9-volt and AA batteries on hand so you do not have to run to the store when a detector chirps. Store them in a cool, dry place—not in a damp bathroom or near a heat source. Check the expiration date on the package; batteries stored for years can lose charge.

Frequently Asked Questions

Why does my First Alert detector chirp even after I put in a new battery?

A single chirp when you close the cover is normal and means the battery is seated correctly. If it chirps every 30 to 60 seconds, the detector may be too old to work properly, or the battery may not be making good contact. Open the cover, remove the battery, and reinsert it firmly. If it still chirps, replace the detector.

Can I use rechargeable batteries in my First Alert smoke detector?

No. Rechargeable batteries lose charge faster than alkaline batteries and may not power the detector reliably when you need it. Always use alkaline batteries—they are inexpensive and last much longer in smoke detectors.

What if I cannot get the cover off?

Do not force it. If the cover is stuck, try turning it more slowly or checking for a clip or latch you may have missed. If it is truly stuck, the detector may be damaged. Replace it rather than risk breaking it further.

Do I need to test the detector after I change the battery?

Yes. After you install the new battery and close the cover, press and hold the test button on the detector for a few seconds. It should sound a loud alarm. If it does not, the battery may not be seated correctly—open the cover and try again.

How do I know what size battery to buy if I am at the store?

Take a photo of the inside of your detector before you leave home, or write down the model number and battery type. If you forget, call the store and describe the detector, or buy one of each type (9-volt and AA) and return the one you do not need.