According to David Fincher, Kristen Stewart grew more than three inches during filming of this project. She was smaller than Jodie Foster when the production started and towered over her when the final shots were done.
The shot of Sarah's medical bag sliding along the floor outside the panic room took 103 takes.
The photos of Sarah that Meg puts around her room are real childhood pictures of Kristen Stewart and her family.
Because the sets had been designed with Nicole Kidman in mind, who is much taller than Jodie Foster, the green safety lasers on the panic room door ended up exactly at the level of Foster's eyes, constantly blinding her as she entered and exited the room.
All of the indoor scenes were shot entirely in the sequence in which they appear in the finished film.