Product DescriptionKidde's Nighthawk 9000234 AC POWERED, PLUG-IN CARBON MONOXIDE ALARM now has a 40% longer life than other CO alarms! It comes with a 9V battery (included) backup and a digital display for continuous easy viewing. The Digital display also adds an advanced level of protection by allowing you to see changes in CO levels in PPM. The new unit even lets you know if it's been unplugged or has come loose from the outlet. Other features include a Peak Level Button, Test/Reset Button and an End of Life Alarm, alerting you when it's time to replace the unit. Seven-year limited warranty.