I have no idea what it is and googling has not helped. It doesn’t look electronic but could be.
Would appreciate advice - thanks.

Sometimes I just sit and think. Other times I just sit.
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Could be HRV or some other sort of ventilation.
Does your house have an alarm system? It could be the inside siren.
Almost certainly siren for the alarm.
Set it off and you'll find out...
Alarm siren for sure.
Have one very similar.
Nothing is impossible for the man who doesn't have to do it himself - A. H. Weiler
We have one of those. Its only in the lobby hallway downstairs, and on a wall not ceiling , so I'd strongly assume its the alarm. It will be loud downstairs, and filter up the stairs easily.
Alarm is my pic
Sometimes I just sit and think. Other times I just sit.
Techinical term is "piezoelectric siren"
Internal siren for burglar/fire alarm system. We have one identical to that
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