HM-803 This smoke alarm features a dual-power design with AC220V mains supply and a DC9V backup battery. It is normally powered by mains electricity and automatically switches to battery power during outages to ensure uninterrupted monitoring. The device sensitively detects smoke concentration and triggers an immediate sound-and-light alarm when abnormalities occur. Easy to install and stable in operation, it is suitable for homes, shops, offices and other scenarios, providing round-the-clock fire safety protection.