Due to the film's meager budget, cast members had to perform their own stunts with little preparation or training. According to Robert Hutton, this almost led to disaster at least once during the shoot. John Agar very nearly overturned a jeep carrying himself and Hutton during a scene in which he was instructed to brake and swerve sharply. The jeep tilted onto two wheels and very nearly toppled over with the actors inside.
The plane crash was from remote control experiments made by the Air Force.
The footage of a car crashing into an electrical substation is recycled from the end of Thunder Road (1958).
Bronson Canyon in Los Angeles served as the location for the stronghold featured in the last third of the film.
The decision to make the aliens invisible was more than a simple plot point. Producer Robert E. Kent insisted that the alien invaders remain unseen in a cost-saving measure. Without costly special effects, extras, and additional sets, the producer's decision helped to balance the film's otherwise severe lack of funds.