Alarms chirp at night for a slightly unfair reason: cool air lowers battery output, so a dying battery crosses the warning line at the coldest hour. A single chirp every 30–60 seconds is a low-battery signal — replace the battery even if the test button still sounds the alarm. It “working” when tested doesn’t mean it works at capacity.
Check the date while you’re up there. Smoke alarms expire: most are rated for ten years from the manufacture date printed on the back, after which the sensor itself is unreliable. An alarm past its date gets replaced, not re-batteried.
Test monthly with the button, vacuum the vents once or twice a year, and keep alarms on every level, inside bedrooms, and outside sleeping areas.
Can’t reach them safely, or you’d rather the whole set was checked and swapped in one go? That fits neatly into a CMG Bridge visit — $125 for the first hour, Staten Island only.