Open the alarm and locate the battery compartment

Most First Alert smoke alarms have a battery compartment on the back or bottom of the unit. Look for a small door or panel that slides or twists open — you do not need tools for this. The compartment will show you exactly which battery type the alarm uses, printed right on the inside of the door or on the battery holder itself.

If your alarm is mounted on the ceiling, you may need a step ladder to reach it safely. Gently twist or slide the alarm counterclockwise to remove it from the mounting bracket, or press the release tabs on the sides if your model has them. The battery compartment becomes accessible once the alarm is in your hands.

Remove the old battery and note its size

Pull the old battery straight out of its holder. Most First Alert alarms use either a 9-volt battery (the rectangular kind) or two AA batteries, depending on the model. The battery holder itself is labeled with the correct size, so you know exactly what to buy as a replacement.

Check the expiration date on the old battery before you throw it away — if it expired years ago, that explains why the alarm has been chirping. Dispose of the old battery at a hardware store, electronics retailer, or municipal hazardous waste facility rather than in the trash.

Key Takeaways

  • Remove the alarm from its ceiling mount by twisting it counterclockwise or pressing the release tabs, then open the battery compartment on the back or bottom.
  • First Alert alarms use either a single 9-volt battery or two AA batteries, and the compartment door tells you which type your model needs.
  • Insert the new battery with the positive and negative terminals facing the correct direction — the holder shows you which way they go.
  • Test the alarm when ready after installing the new battery by pressing and holding the test button until the alarm sounds.

Insert the new battery the correct way

Buy a fresh battery of the correct size and type. For a 9-volt battery, slide it into the holder until it clicks or sits firmly in place. For AA batteries, insert them one at a time with the positive end (marked with a + sign) facing the direction shown in the battery holder — usually toward the spring or metal contact.

Do not force the battery in. If it does not slide smoothly, you may have the polarity backwards. Remove it, flip it around, and try again. Once both batteries are seated properly, you should hear or feel a small click.

Close the compartment and reinstall the alarm

Slide or twist the battery compartment door back into place until it clicks shut. Then reinstall the alarm on its ceiling mount by twisting it clockwise until it stops, or by pressing it firmly into the bracket until the tabs lock. The alarm should sit flush against the ceiling with no gaps.

If your alarm was hardwired to your home's electrical system in addition to having a battery backup, the battery change does not affect the wiring — the alarm will continue to draw power from both sources.

Test the alarm to confirm the battery is working

Press and hold the test button on the front of the alarm for three to five seconds. The alarm should sound a loud chirp or beep — if it does not, the battery may not be inserted correctly. Remove the battery, check the polarity again, and reinstall it.

If the alarm still does not sound after a second attempt, the new battery itself may be defective. Try a different battery from a different package or store. Once the test button produces a loud sound, the alarm is working and the battery is installed correctly.

When to replace the battery again

Most smoke alarm batteries last between six months and one year, depending on the model and how often the alarm runs self-tests. First Alert alarms will chirp once every 30 to 60 seconds when the battery is low — this is the signal to replace it soon, not an emergency.

Mark your calendar or set a phone reminder for six months from today so you remember to check the battery before it starts chirping. Some people change their smoke alarm batteries when they change their clocks for daylight saving time, which happens twice a year and is straightforward to remember.

Frequently Asked Questions

Why is my First Alert alarm chirping even after I put in a new battery?

The chirp usually means the battery is low or not fully seated. Remove the battery, check that the positive and negative terminals are facing the right direction, and push it in until you hear a click. If it still chirps after the test button sounds loud, the new battery may be defective — try a different one.

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

Most First Alert models are designed for single-use alkaline batteries only. Rechargeable batteries may not provide consistent power and can cause the alarm to malfunction or fail to sound during a fire. Stick with standard alkaline 9-volt or AA batteries from a hardware or grocery store.

What if the battery compartment is stuck and will not open?

Do not force it — you may crack the plastic. Try gently wiggling the door or panel while you twist or slide it. If it remains stuck, the alarm may be old enough that the plastic has warped. Contact First Alert customer service with your model number, or consider replacing the entire unit if it is more than ten years old.

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

No. Hardwired smoke alarms stay powered by your home's electrical system while you change the battery backup. The battery change is a straightforward swap and does not require you to touch any wiring or circuit breakers.