We had hard wired ones upstairs which we disconnected and installed regular smoke alarms . . .the hard wired ones were a PITA!!!
They would go off literally in the dead of the night . . .no fire, no smoke, nothing . . changed the batteries, vaccumed in case there were cobwebs or a spider, but they did it even after that . . .on occasion . . .always between 2 to 4 am . . .it was annoying and spooky all at the same time . . .
