Kidde 21009720 Worry Free 10-Year Lithium Ion Battery Operated CO Alarm with Digital Display Kidde 10 year carbon monoxide alarm is maintenance-free; never replace a battery during the alarm's operating life Features an end-of-life signal that alerts you when it is time to replace the alarm; signal chirps every 30-45 seconds when alarm needs replaced Money savings, no batteries to buy and replace every six months, save up to $40.00 over the life of the alarm