First Alert Smoke Alarm 9120B Battery Replacement

Introduction

Follow this guide to fix your First Alert Smoke alarm. This fix will stop the First Alert Smoke alarm from beeping when your battery is low.

Make sure you have your 9V battery in hand and a helper to make sure that you do not fall from your stool. These alarms are usually found mounted into your ceiling so please take precautions when unmounting the alarm.

As you will be working with wires, please make sure that you are gentle with the alarm since it is easy to break the covered wires if you are too aggressive with it. All of these steps should require very little strength. If you find yourself needing to force things into place, please review the steps to make sure you are properly uninstalling/installing the smoke alarm.

What you need

Step 1 Battery

First Alert Smoke Alarm 9120B Battery Replacement, Battery: step 1, image 1 of 3

First Alert Smoke Alarm 9120B Battery Replacement, Battery: step 1, image 2 of 3

First Alert Smoke Alarm 9120B Battery Replacement, Battery: step 1, image 3 of 3

Remove the alarm by rotating it counter clockwise in the mount.
The alarm should fall off once rotated enough. The cable should be the only thing holding it in place if done correctly.

Edit

Step 2

Unplug the cable from the alarm.

Edit

Step 3

First Alert Smoke Alarm 9120B Battery Replacement: step 3, image 3 of 3

Press down on the catch on the top left of the alarm to open the battery compartment.

Edit

Step 4

Remove the battery and dispose of it properly.
Replace the old battery with a new 9V battery and close the compartment.
You should hear a click to know that the compartment is secured.

Edit

Step 5

Line up the holes of the cable on the mount with the pins on the alarm.
Reconnect the cable on the mount to that on the alarm.
It should insert itself with minimal force.

Edit

Step 6

Press the alarm into the mount.

Edit

Step 7

First Alert Smoke Alarm 9120B Battery Replacement: step 7, image 3 of 3

Rotate the alarm clockwise until it does not turn anymore. This makes sure the alarm is secured.

Edit

Finish Line

One other person completed this guide.

Author

with 2 other contributors

Miggy Reyes

Member since: 02/15/21

219 Reputation

1 Guide authored

Badges: 7

+4 more badges

Team

Texas Tech, Team S3-G17, Cowan Spring 2021 Member of Texas Tech, Team S3-G17, Cowan Spring 2021

TTU-COWAN-S21S3G17

1 Member

3 Guides authored

5 Comments

How do I disconnect the cable? Seems very tight and cannot disconnect.

Jeanne O - Nov 22, 2022 Reply

This is related to first alert smoke alarm 9120B. Can not remove connecting cable from alarm. Is very tight. So unable to change battery. Any suggestions?

Jeanne O - Nov 22, 2022 Reply

These alarms suck! Pressing the tab and the battery compartment does NOT pop open. I needed a knife to pry it open, and then it had to be forced close. NOT user error! The plastic pins that hold the battery compartment closed don't move out of the way enough to allow opening.

James Durso - Sep 26, 2023 Reply

I replaced the battery and it is still beeping, reset the smoke alarm. What should I do now?

Donald Sandford - Nov 3, 2023 Reply

Buy and install a new alarm. It’s easier than trying to fix on.

Stephen Taylor - Dec 31, 2023 Reply

First Alert Smoke Alarm 9120B Battery Replacement

Introduction

What you need

Step 1 Battery

Add Comment

Step 2

Add Comment

Step 3

Add Comment

Step 4

Add Comment

Step 5

Add Comment

Step 6

Add Comment

Step 7

Add Comment

Author

Miggy Reyes

Team

Texas Tech, Team S3-G17, Cowan Spring 2021 Member of Texas Tech, Team S3-G17, Cowan Spring 2021

5 Comments

Add Comment

Embed this guide

Preview