Most people have heard the popular police 10-4 code, which means the responder got the message and understands it, according to RadioLabs. One of the more known codes is 10-20, which asks for a location. When an officer is down, another officer broadcasts 10-00 to get all units to respond. Police added the 10 to the beginning of the main codes to offset the effects of radio transmission static in the 1920s and 1930s, explains Timothy Roufa for About.com.
Other frequently used 10 codes include 10-8, which means the officer is available for calls, and 10-13, which is a way for a dispatcher to check on an officer. It may also refer to other conditions, such as weather, crowds and status of an individual, according to Roufa.
Some 10 codes include letters of the alphabet. For example, 10-15 means a prisoner is in custody, but if the prisoner is mentally incapacitated, the officer uses code 10-15m, notes RadioLabs. The check for wants request is 10-29, but there are seven additional 10-29 codes, which include letters, such as 10-29F. This means the subject is wanted for a felony. When a subject is wanted for a misdemeanor, the officer says 10-29M.
Codes regarding criminal activities or warnings include 10-71, which means a shooting is involved; 10-73 indicates a gun is involved; 10-79 is a bomb threat; and 10-80 refers to an explosion. When death and near-death situations are involved, some of the codes include 10-32 for a drowning, 10-56 for a suicide and 10-56A for a suicide attempt, explains RadioLabs.