When activated, all smoke detectors in your home alarm simultaneously. Difficult-wired detectors are normally on and when the ability goes out, the battery backup kicks in.????? ????? ??????? ??????? ??? ??????? ???????? ???????? (??????? ?? ????????????? ????? ?? ????? ???????? ???????????? ????? ???? ?? ???? ?????? ????? ?? ????? ??? ?????? ????