10-4: A Look at the Meaning Behind This Common Phrase

10-4 is the code word for “affirmative” or “understood’ in the brevity code used mainly by law enforcement, first responders, and Citizens Band (CB) radio transmission. It is used as a standard of shortened communication.

Read on to learn more about the brevity ten codes, including their history and a list of the codes!

History of Brevity Standard

The Association of Public-Safety Communications Officials-International (APCO) developed a set of brevity codes between 1937 and 1940. The codes were used as a shortened form of speech traffic, hence the name brevity codes.

The recommendation from APCO was not only to use the codes in place of language but also for police to create their standard arrangement for the context of messages. For example, an officer reporting on a suspect would follow the standard of age – height – shirt color – pant color.

The Ten Codes

The idea for the Ten Codes is credited to Charlie Hopper, the communications director for the Illinois State Police. In 1937, police radio channels were limited and the first syllable of spoken words was routinely not transmitted.

This was because of the vacuum tubes and dynamo motor used in the radios. It took ¼ to 1/10 of a second to power up, thus the first part of speech was never transmitted.

The Ten Codes were used almost exclusively by law enforcement until 2006. The U.S. Federal Government stepped in to recommend discontinued use of the codes in favor of plain language.

What do the other Ten Codes mean?
The other Ten Codes that are commonly used are

10-7 – out of service
10-12 – standby
10-14 – prepare to copy
10-30 – use caution
10-33 – office down

Are Ten Codes still used today?

Some small law enforcement departments and offices still use Ten Codes today, but the majority of large urban areas have foregone the use. This is because emergency responders have a need for clarifying and direct communication.

With hundreds of new law enforcement officers being recruited and hired weekly, it is impossible for large districts to train everyone properly before sending them out into the field. Therefore the federal government suggested that departments discontinue the use of the codes.

Today, most large law enforcement departments use plain language that any officer, new or seasoned, can understand. This has decreased the amount of miscommunication experienced during calls.