A stop to barricade a door from forced entry. The stop includes an upper portion designed to contact the door to barricade it against forced entry, and a lower portion that fits within a receptacle that is recessed into the floor. The stop can be removed from the receptacle when the user doesn't desire to barricade the door. When the stop is placed in the receptacle, the stop is preferably configurable by the user in two modes: a first that allows the user to slightly open the door by a gap, and a second that barricades the door when it is shut. Barricading the door in this second mode is beneficial because it allows the user to look through the gap to verify the identity of a person on the outside of the door, and/or to receive an item through the gap while not opening the door completely.