Smoke alarm beeps once per day

[JohnW6]

My house has four Nest smoke alarms.  One of them beeps (I think it's a 4-note series) once a day.  These alarms were installed about three years ago, and this behavior just began a few days ago.  The app indicates all is OK, and nothing in the history indicates that any of the alarms have issues.  Yesterday, I used the app to initiate a successful full test of all four alarms.  Today, one of the alarms (still don't know which one) unleashed its brief serenade.  During the day, this is only a minor annoyance, but in the wee hours of the morning, it's enough to wake us up.  Aside from once a day, I've yet to see a pattern in the time at which these little songs are played.  Some days it happens in the afternoon; other days it's in the middle of the night.  And, it always seems to be just once a day, from just one of the four devices.

[Lance_L]

Hi JohnW6,

Thanks for reaching out to the Community and sharing all the details about the issue. I’d be happy to help you with Nest Protect. Let’s check it out.

Here’s a guide to Nest Protect lights and sounds. Does any of those sounds match the one that you hear from the affected device?

Also, can you share a video of the Nest Protect when it is making the sound? Below are the steps on how to upload a photo or video:

• Hit reply or start a new post.
• Click Insert Photos.
• Choose an image source location.
• Follow the on-screen instructions.
• Also, you can tap the "Drag and Drop" option. The maximum attachment is 5 MB.

Keep me posted.

Best,

Lance

[JohnW6]

Thank you for helping with this mystery. 
I think the sound emitted by the affected device(s) is the series of (four, I think) different tones produced at the beginning of a sound-check cycle.  In the case of a sound check, this series is followed by a series (two, I think) of loud high-pitched tones. But, in our mystery case, nothing follows the series of four tones.  I found only sample voice announcements on the referenced web page but no tones.

Since this behavior occurs at unpredictable times, I cannot provide a video or audio recording.