When activated, all smoke detectors in your house alarm at the same time. Hard-wired detectors are normally on and when the ability goes out, the battery backup kicks in.???? ??????? ????? ?? ??????? ???????? ??? ????? ??? ????? ? ????? ??????? ?????? ??? ????? ????? .???? ????? ???? ????? ????? ???? ?????? ???? ?????..???? ????? ?????????? ???????