When fishing down walls from the attic for a keypad or flush-mount speaker, first check with your stud finder to be sure there's no horizontal fire block in the way. Then cut out the hole for the device and leave a pocket Maglight(tm) shining in the hole. When you drill down from the attic you can see the light in the wall to be sure you're in the right place.
On the same note, I always liked to install a flush siren speaker in a load bearing wall at electrical outlet height below the keypad. Whenever possible I would do this on both the main and second floor, one directly above the other. This made easy access to pull cables from the attic to the basement by reaching in and drilling down through the base of the wall cavity to the wall below.