Kidde KN-COB-LP2 Carbon Monoxide Detector, 2 AA Battery Powered (21025788) Battery operated (2AA batteries included) Provides protection during power outage. Low battery hush silences low battery chirp warning for up to 12 hours in order to maintain protection without having to replace the batteries at an inconvenient time Battery lockout system deters covering battery compartment without installation of batteries Event memory: If the unit has detected CO concentrations of 100ppm or greater, the green LED will flash every ten seconds Slide-out battery door cover gives