We have a mysterious beeping/chirping sound that occurs in the house. It starts in the morning usually. Five beeps in a row at a regular interval, then five beats again after about a minute or so. Repeats constantly for a couple of hours, then stops completely. Then a couple of weeks later, it starts again. We installed new smoke/CO alarms recently that work with an app and has voice commands, so it's not that. We don't have a landline, so it can't be a phone connection. There are no children here, so no electronic toys. It seems to be loudest in a bathroom near the vent. What could it possibly be?
If you can hear it coming from a vent, it might be elsewhere. I would keep the bathroom door closed, and during that repeating period drop whatever I'm doing immediately, and try to listen at other places where ventilation ducts pass by. This way you might be able to pinpoint more accurately where it comes from.
Also listen to nearby vents to see how strongly you can hear it. If it's definitely in the ventilation system it would help retrieving the building plans so you can see their paths.