We are having a very infrequent beep occur in the house. It lasts about one second and then stops for a long time, about once an hour or so. I can't tell what direction it is coming from but we have checked all the smoke and carbon monoxide detectors. We can hear it pretty clearly from the living room and dining room.
A once per hour beep sounds a lot like a low battery indicator -- what else do you have running on batteries around the house?
Some things to check:
- Internet/Phone - specifically in my area, Verizon FIOS often has a battery backup so that phones don't go out when the power goes out in order to better simulate POTS Actually, in many recent FIOS installations they haven't bothered because people wouldn't bother to replace the batteries.
- Burglar Alarm
- UPS - Typically attached to a computer
Another idea: a service reminder built into an appliance or as a separate small battery-powered device. It could be a reminder to check the salt level in a water softener or to check the filter in the furnace, for example.
Make note of the exact time when you hear the chirp a couple times. Compute the interval and check whether it is consistent (it probably is). Then you can forecast when a future chirp will occur and can be ready to listen for it and localize the source better.