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Police scanner codes, most commonly called 10-codes, are shorthand phrases used by law enforcement, fire departments, and EMS over radio.
They were first developed beginning in 1937 by the Association of Public-Safety Communications Officials (APCO) and later refined and expanded in the 1970s as radio systems evolved. The goal was simple: keep transmissions short and clear on early AM radio channels that had limited bandwidth and slow push-to-talk switching.
Instead of saying "I understand your message," an officer says 10-4. Instead of asking "What's your location?" dispatch says 10-20.
If you listen to a police scanner app, understanding these codes makes the difference between following the conversation and hearing confusing radio chatter.
APCO published more than 100 codes, but most agencies only use a small subset. These are among the most widely heard across the United States:
After a few listening sessions, these become surprisingly easy to recognize in real time.
Here's what surprises most new listeners: there is no universal set of 10-codes.
While APCO created a recommended list, many agencies modified or replaced codes over the years. The same number can mean different things in different places. Some departments even created their own entirely separate code systems.
When you tune into a new city or county feed, expect a short learning curve.
A major turning point came after Hurricane Katrina in 2005. During the multi-agency response, responders from different jurisdictions often couldn't understand each other's radio codes.
Afterward, the U.S. Department of Homeland Security encouraged agencies to use plain language for major incidents and interagency communication, saying "robbery in progress" instead of a code number.
Many departments have since adopted a hybrid approach:
For scanner listeners, this is good news. Modern radio traffic often includes a mix of both, making it easier to follow than in the past.
The best way to learn police scanner codes is to hear them in context. Open Scanner Radio, find a busy feed in your area, and listen for a few minutes. You'll be surprised how quickly it clicks.