Kidde Sealed Lithium Battery Power Carbon Monoxide Alarm with Digital Display  C3010D LED Lights - Green for normal operation, Red for alarm, Amber for Error. Digital Display - Displays the level of carbon monoxide the unit is sensing. The unit updates this reading every 15 seconds. 10-Year Sealed-in Lithium Batteries -Unit will continue to operate for 10 years. Alerts user to replace unit after 10 years of operation. Peak Level Memory - Displays the highest CO concentration measured since the last reset. Test/Reset -Tests CO alarm circuit operation and allows you to immediately silence the alarm.