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 is usually labeled with a battery symbol or the word "Battery" printed directly on the plastic.

If your alarm is mounted on the ceiling, you may need to remove the entire unit first. Grasp the alarm body firmly and twist it counterclockwise (or pull straight down, depending on the model) to separate it from the mounting bracket that stays attached to the ceiling. Once the alarm is in your hand, the battery compartment becomes straightforward to access.

Remove the old battery

Open the battery compartment door by sliding it to the side or twisting it, depending on your model. You will see a battery sitting in a plastic holder or slot. The battery is usually a 9-volt rectangular battery, though some First Alert models use AA or AAA batteries instead.

Note which direction the battery is facing—the positive terminal (marked with a + sign) should be pointing toward the spring or contact inside the compartment. Gently pull the battery out by gripping it at the edges. If it is stuck, wiggle it slightly side to side rather than yanking hard.

Key Takeaways

  • Most First Alert alarms use a 9-volt battery, but check your model number or the compartment label to confirm the correct size before buying a replacement.
  • The battery compartment door slides or twists open without tools, and the entire alarm may need to be twisted off the ceiling bracket first.
  • Insert the new battery with the positive terminal facing the spring contact, and push gently until you hear or feel a click.
  • The alarm will chirp or beep once when the battery is installed correctly, confirming the connection is find.

Insert the new battery

Take your new battery and check the label to confirm it is the correct size for your model. Hold the battery so the positive terminal (the + side) faces the spring or metal contact inside the compartment. Slide the battery into the slot and push gently until it sits flat and makes contact with the spring.

You should hear a single beep or chirp from the alarm when the battery makes a good connection. If you do not hear a sound, remove the battery, check that the positive terminal is facing the right direction, and try again. A beep means the alarm recognizes the new battery and is working.

Close the compartment and reattach the alarm

Slide the battery compartment door closed or twist it shut until it clicks into place. The door should sit flush with the alarm body with no gaps. If the door does not close smoothly, remove the battery and check that it is seated properly in the slot—a battery that is not fully inserted will prevent the door from closing.

If you removed the alarm from the ceiling bracket, hold the alarm up to the bracket and twist it clockwise (or push straight up) until it locks into place. You should hear or feel a click. The alarm is now ready to detect smoke.

Test the alarm after battery installation

Most First Alert alarms have a test button on the front or bottom of the unit. Press and hold this button for three to five seconds. The alarm should sound loudly—a loud, continuous beeping. If it does not sound, remove the battery, wait ten seconds, and reinsert it, then test again.

If the alarm still does not sound after reinserting the battery, the battery itself may be dead or defective. Try a fresh battery from a different package. If a new battery does not work, the alarm may have reached the end of its life and may need to be replaced.

What to do if the alarm keeps chirping after battery replacement

A single chirp or beep every 30 to 60 seconds usually means the battery is low or not making good contact. Remove the alarm from the bracket, open the battery compartment, and check that the battery is pushed all the way in and the positive terminal is facing the spring. Reinsert the battery firmly and test again.

If the chirping continues after you have reseated the battery, try a brand-new battery from a fresh package. Batteries can be defective even when new. If a fresh battery still produces chirping, the alarm's internal sensor may be failing, and the unit should be replaced.

Frequently Asked Questions

What size battery does a First Alert smoke alarm use?

Most First Alert models use a 9-volt battery, but some use AA or AAA batteries. Check the label inside the battery compartment or look up your model number on the First Alert website to confirm before you buy. The model number is usually printed on the back or bottom of the alarm.

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

No. First Alert alarms are designed for single-use alkaline batteries only. Rechargeable batteries do not hold a consistent voltage and may not power the alarm reliably. Always use a fresh alkaline battery of the correct size.

How often should I replace the battery?

Replace the battery once a year, or whenever the alarm chirps to signal low battery. Many people change their smoke alarm batteries when they change their clocks for daylight saving time, which makes it straightforward to remember. A fresh battery ensures the alarm will work if smoke is detected.

Why is my alarm still chirping after I put in a new battery?

The battery may not be making good contact with the spring inside the compartment. Remove the alarm, open the battery door, and push the battery all the way in until you feel it click or seat firmly. Make sure the positive terminal faces the spring. If chirping continues with a fresh battery, the alarm itself may need replacement.

Do I need to turn off the alarm before replacing the battery?

No. Smoke alarms do not have an on-off switch. You can replace the battery while the alarm is mounted on the ceiling or after you remove it. The alarm will not sound during battery replacement unless you press the test button.