- During the parking garage sequence, a yellow Lincoln Continental sedan plays an important part in the during the attempted bombing of the Hyatt Regency Hotel in Houston Texas (actually San Francisco, California). In Charley Varrick (1973), also directed by Don Siegel, a yellow Lincoln Continental was used during a bank robbery, where the driver, played by Jacqueline Scott (I) is wounded and dies.
- Charles Bronson and Donald Pleasence appear together for the last time.
- The interior of the Hyatt Regency is located at 5 Embarcadero Center in San Francisco, California. This is the same location where Towering Inferno, The (1974) was filmed.
- - The code used to activate sleepers is taken from a poem by Robert Frost, "Stopping By Woods on a Snowy Evening", originally published in 1923 in his collection titled "New Hampshire". The exact lines are: The woods are lovely, dark, and deep, But I have promises to keep. And miles to go before I sleep, And miles to go before I sleep.
- When Bronson encounters Immigration on the Canadian border, the agent asks his character's citizenship and birthplace, to which he responds, "American, from Pennsylvania" Charles Bronson's true birthplace.
- Don Siegel asked Bronson to shave his trademark mustache. Bronson replied, "No mustache, no Bronson."
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