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Changing the battery on Gentex 7139CS-C Smoke Alarm

I hate dealing with situations like this so I’m creating this post to hopefully help other people. Although, once you make it far enough to even find this post you’ll probably have the problem solved.

The Model

Here is a picture of my Smoke Alarm… The model number is not anywhere on the outside of the detector! So you’re left searching for the various Gentex detectors.


You can see that it is a Gentex, but there is no model number. And here’s what this looks like on the Gentex site as of this writing:


It was a bit challenging to recognize…

To Gentex’s credit, here is a link to their documentation. And here is the section on their on changing the battery:


The words are good, but pictures certainly help…

Getting the Alarm Off

You do need to do just as they say, rotate counter-clockwise.

Then keep rocking gently to unsnap the AC power connector. Here’s what the AC power connector looks like:


They did a nice job and there is only one way for it to fit back in, so you don’t need to worry about keeping track of how you had it plugged in.

Getting the Battery Out


Once you have the alarm off and are safely off the ladder, you simply rotate the red arm that covers the battery. Once you do that, you may need to use something thin like a knife to let push the battery out. My battery would not simply drop out. Here is a side view of the battery and you can see that you can push it out by sticking a knife through the slots:


When you have the battery out it will look something like this:


Now simply replace the battery. It is a 9 volt battery. The instructions say that you must use a Duracell MN 1604. I’m not sure why, but it just so happened that I had that exact model in my battery collection.

Putting It Back On

That should be easy, but it took quite a bit of effort to get the alarm back on by lining it up and and now turning clockwise.

If this doesn’t help others, at least I’ll have a reference for myself with the battery runs down on my alarms again.


  1. Amy says:

    I’m eternally in your debt! After dozens of attempts on my own over the last 2 days and going bonkers listening to that chirping, I google instructions and found your helpful hints.THANK you, THANK YOU!!

  2. Linda says:

    Thank god you put this up! Couldn’t find any site that told me how to change battery, your a life saver.

  3. karlz says:

    It is tricky and I always felt like I was going to break something. Not sure why they don’t have better instructions on their site.
    Actually, each time I need to change mine I come back to this site… It’s too complicated to remember something you do once every 18 – 24 months.

  4. Jenny C says:

    Thank you! Once i removed the wall plate, I could get to battery – ours did not have red arm. It was easier to stick battery in slot and then snap conductor back on. I really appreciated the information.

  5. karlz says:

    For future reference, mine were manufactured Dec 2006.

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