BRK 4120B

I have a new house with about 10 of these interconnected. over the past few nights they started going off (sounding the alarm) for about 30 seconds then stopped. I removed them one at a time (unplugged completely from the ceiling). and when the noise stopped I left the rest operational. last night I got up twice when they started sounding off and removed a few each time which quieted them up for a few hours each time. finally I removed them all.

No, my house was not on fire.

it only happens at night, batteries are good, I didn't notice which one had the blinking red light but I know it was more than 1.

what shuts these off after 30 seconds? was this a true detection? could it be caused by dust buildup? they were installed 1.5 years ago.

HELP!