Digital display stores, recalls & displays highest level of co detected. No installation required, can be placed anywhere. Test button. silence button for unwanted alarm & for low battery warning signal. Low battery warning signal. easy battery replacement (compartment on the front). User-friendly action chart detailing what to do in case of alarm. Led for power, service & alarm. easy to install with 2xaa battery (with a minimum of 1 year life) & fittings included. loud 85 decibel alarm.