First Alert, 120V Electrical Plus Battery Back Up Smoke Alarm, Ionization Technology, For 120v Ac Wired In Applications, Alarm Silencer Feature, Universal Mounting Bracket, Pivoting Side Load 9V Battery Compartment, Interconnectable Up To 18 Multiple Station Alarms, When 1 Alarm Sounds, They All Sound, 9V Battery Included, 10 Year Limited Warranty, Approved For Sale In Oregon After Revisions To Governors Law, Replaces #SA4121CN .