When activated, all smoke detectors in your house alarm concurrently. Really hard-wired detectors are usually on and when the facility goes out, the battery backup kicks in.???? ?? ??? ????? ???????? ?? ????? ?? ???? ???? ????? ?????? ??? ???? ????? ?????? ?? ???? ????? ????? ??? ????? ?????? ?????? ??? ?????? ?????? ?? ????????? ?????? ??? ???? ??