When brought on, all smoke detectors in your home alarm concurrently. Really hard-wired detectors are normally on and when the power goes out, the battery backup kicks in.????? ?????????? ??? ???? ???????? ?????? ???? ???????? ?? ??????? ??? ??? ?????.????? ??? ????? ????? ???? ??????? ?????? ????? ?????? ??? ???? ????? ?????? ????? ??????? ???????