White Heat, a 1949 gangster film starring James Cagney, reached its climax with a police chase. Unbeknownst to Cagney's character, an undercover cop had wired his car with a radio oscillator. The police used two cars outfitted with directional radio receivers, allowing them to triangulate the location of the fleeing car. The end result was ... explosive.
Radio triangulation had been in use for a while, but seeing it applied to an urban environment to track a vehicle was amazing in 1949. It gave the public a window into the latest law enforcement technology--something that gangster films have been famous for over the years.