Different Beeps on Smoke Detector/ Carbon Monoxide Detector?

I m not sure if I should be concerned for the neighbors house. As far as I know, no one is living there but I was woken up by the sound of beeping,

3 Beeps, Pause, 2 Beeps, Pause, 3 Beeps, Pause, 1 Beep

3 Beeps is always the alternate one, The other two are inconsistent.

Is this any cause for concern?
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