In the opening scene, one of the callers in the 911 center states "I think I'm having an overdose and so is my wife." The line was made famous by Edward Sanchez, a policeman who confiscated marijuana from a suspect and then made brownies with it. He called 911 when he thought he had taken too much.
Halle Berry visited a call center and shadowed 911 operators in preparation for her role. She found their job to be very emotionally stressful.
Screenwriter Richard D'Ovidio got the idea for the film when his wife saw an interview with a 911 operator on TV. Researching the subject, he visited the Los Angeles Metropolitan Communications Dispatch Center and was surprised to find that it had its own back-up generators, bulletproof windows and a moat.
Originally envisioned as a TV series called "The Hive".
Halle Berry was initially cast in the lead role with Joel Schumacher directing. Schumacher dropped out and was replaced by Brad Anderson. Berry dropped out due to scheduling conflicts but once the start date was pushed up, she returned in the lead role.