Ten-codes, also known as 10-codes or ten signals, are code words used by many police officers to aid with voice communication. The codes were originally developed in 1937 to allow for brevity, clarity, and standardization of messages transmitted over radio channels. On old radio systems, channels were limited so messages needed to be short. Also, the first syllable of speech was often not transmitted, so the syllable “ten” was prefixed to all numeric codes to ensure that the important information would be received.

Despite their usefulness, the exact meaning of ten-codes often varies between jurisdictions and locations. In addition to law enforcement, ten-codes are frequently used on Citizens’ Band (CB) radio. One of the most frequently used ten-codes, 10-4, has become popular enough to sometimes be used in every-day language.