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.
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.
Nicole Kidman was originally cast in the role of Meg Altman and Hayden Panettiere was cast as her daughter, Sarah. Before filming began, Panettiere was replaced with Kristen Stewart as director David Fincher found her "irritating". Then, only eighteen days into filming, Kidman had to leave the film as well, due to a recurring knee injury, suffered during the filming of Moulin Rouge! (2001). Fincher suggested that the studio close the production and collect the insurance, but the studio decided to go on. Jodie Foster was offered the role. She was due to be the president of the Cannes Film Festival jury but withdrew to work with Fincher, with whom she was originally supposed to work on The Game (1997) in the role now played by Sean Penn. Foster had only nine days to prepare for the role. Kidman left a small mark in the film nevertheless, however, as the voice of the girlfriend of Foster's husband in the movie, heard answering the phone when Foster's character calls him in a desperate attempt for help.
David Prior, who produced the film's DVD noted that this was "the most elaborate, complex DVD I have yet produced." According to Prior, director David Fincher originally conceived the film as a low-budget B-film. But during the process it evolved into a "gargantuan undertaking that tested the endurance and tenacity of everyone involved."
Though Panic Room is not technically a remake, it somewhat mirrors the plot and characters of Wait Until Dark (1967). The antagonists are three criminals: one who has compassion like Burnham, another who is a hardened criminal like Junior, and one who is a ruthless psychotic like Raoul. The three men charade their way into a blind woman's brownstone apartment in search of a doll filled with heroine, but they realize they have drastically underestimated her wits once they initiate a game of cat and mouse with her.
Jodie Foster was pregnant with her second child during filming. Because of this, reshoots had to be made in the autumn of 2001 after she had given birth, as principal photography took longer than planned.
Forest Whitaker's character was initially imagined by screenwriter David Koepp as an unpleasant white-collar compulsive gambler, in Koepp's own words someone like "Humphrey Bogart in one of his less pleasant roles."
David Fincher agreed that the film's production was an arduous one, remarking it as a "logistical nightmare." The lighting issue during the filming process was particularly difficult due to the complexity of the security cameras used in the mansion that send surveillance images to the television in the panic room.
The trivia item below may give away important plot points.
In a previous draft of the script, the final battle is completely different. As Sarah is being held hostage in the panic room with Raoul and Burnham, Meg gets out of the house, enters the next door house, adjacent to hers, breaks into the panic room through the dividing wall with the sledge hammer and fights with Raoul after Burnham gets the bonds and runs down the stairs. Raoul is killed by the panic room door slamming on his head, and Burnham is shot and killed by the police in the foyer of the house as he is fleeing.