OMEX 205 DC Wireless Long Life Smoke Alarm For Residential Applications provides battery-powered smoke detection and alarm functions within a single unit. Advanced electronics in conjunction with a photoelectric smoke sensing chamber provide early detection of fire and high immunity against unwanted alarms. 205 DC smoke alarms are powered by a long-life lithium-ion battery and do not require a mains supply. Models with either user-replaceable and non-replaceable batteries are available. Interconnectable 205 DC smoke alarms use a wireless transmission path. Configuration into a closed group ensures that other units within the radio signal range are not affected by a test or fire alarm occurring within the configured group.