CAUTION : Align the Interior Unit while the Thumbturn Lever is open position [Right-handed] [Left-handed] 2) Open the battery cover of the Interior Unit. (There are the screw grooves at the upper left and right corners) Using two FH+M4 x 8 screws, fasten the upper portion of the Interior Unit (a) Using two FH+M4 x 8 screws, fasten the lower portion of the Interior Unit (6b). 7. Install 4 Alkaline batteries. A melody will sound when all 4 batteries are installed correctly. CAUTION: Press the [OPEN/CLOSE] button to check whether the deadbolt works properly.