Important: as you can see in the pictures there needs to be
a small space (about 1/8") below the door for the base of the DoorJammer
to slide under. This space is normally found under interior doors but not under
all exterior doors.
The Greater the Force of the Attempted Entry, the Stronger it Holds
The horizontal force being exerted on the door from the
outside is converted into a vertical force to anchor the DoorJammer firmly into
the ground. Not only does this prevent the door from moving
horizontally, it also forces the door upward, increasing the DoorJammer's grip
and reducing the chances of its foot slipping on the floor.