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