As a homeowner, you should reset the opener to prevent outsiders from opening the door with a remote that's set to a Liftmaster default code. A simple procedure allows you to reset the opener for one or more remotes.
doorsill - the sill of a door; a horizontal piece of wood or stone that forms the bottom of a doorway and offers support when passing through a doorway. doorstep, threshold. 1  doorway, room access, door, threshold - the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close; he stuck his head in the doorway.
1 Beneath some thresholds is a portion of the door frame known as the sub sill. Check the sub sill as well as you install the sill above it to ensure that it is in good condition.  Always make sure you replace the sill with one of the same size and shape, including thickness.