The FireAngel alarm uses electrochemical sensing technology to detect carbon monoxide quickly. It spots rising CO levels early and prompts you to ventilate in time. And if it sounds while you're out, the alarm memory keeps track, so you will know what happened. Good to know - It uses replaceable AA batteries, so you can swap them out whenever needed - With Sleep Easy mode, low-battery warnings are limited overnight - Smart Silence helps stop false alarms without fully switching it off - The loud 85 dB alarm makes sure everyone at home hears it straight away