We have been having the a similar problem. A very intermittent chirp, maybe once an hour, from one of our alarms that my wife can hear but I can't.
I changed one in the hallway but two more are way up at about 15 feet and it might be one of them although new ones were installed only about a year ago. There are also batteries in the thermostat and it showed they were low, so I changed those out this morning. Waiting to hear iffn the chirping has stopped yet. π€¦
deadeyedick wrote: