CB radio is a set of forty audio channels set aside by the Federal Communications Commission so that individuals may broadcast short messages to listeners over a range of a few miles. No license is required to use CB radio. Though widely remembered as a fad, CB radio is still used to communicate information between drivers on US highways.

CB channel 9 is designated for emergency services and is especially important in areas where regular telephone service is unavailable. CB radio enthusiasts contributed the phrase “10–4” (the term signifies agreement with a speaker) to the American vocabulary.