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All cast members were required to have their hair trimmed every five days.

Kiefer Sutherland has said in many interviews that he is not the star of the show: the time element is.

In the fifth episode of the fourth season, Debbie's cell phone rang with a valid California phone number on the caller ID. Many fans noticed this and called the number, Some callers heard a voice mail message telling them that they called the 24 prop phone and to leave a message. Others spoke with various people, including Production Designer Joseph A. Hodges and stars Kim Raver (Audrey Raines) and Carlos Bernard (Tony Almeida). Hodges later stated in an interview that director Jon Cassar came up with the idea for the "Fan Phone" because the two of them often got bored scouting new shooting locations and wanted a chance to interact with the audience. Hodges indicated they received around 80,000 calls on the line in the first week.