In APCO, Association of Public-Safety Communications Officials 10-codes, 10-4 means "Acknowledgment" or "Message Received". It is used to confirm that a transmission has been heard and understood, without necessarily implying agreement or compliance.
Here’s how it might be used in a real-world scenario:
- Dispatch: "Unit 12, respond to a disturbance at Maple and 3rd."
- Officer: "10-4."
In this exchange, the officer is acknowledging receipt of the message (10-4), confirming that the instruction was heard and understood.
Because 10-4 communicates acknowledgment without adding unnecessary detail, it helps keep radio traffic concise and efficient.
Historical Background
The use of 10-4 dates back to the original APCO 10-code system, developed to improve clarity and efficiency in early two-way radio communications. At a time when radio channels were noisy and bandwidth was limited, short numeric responses reduced airtime and minimized misunderstanding.
Acknowledgment codes like 10-4 allowed dispatchers to quickly confirm that messages were received without requiring full verbal repetition, which was especially important during busy or emergency situations.
Operational Usage
In daily operations, 10-4 is one of the most frequently used 10-codes. It may be transmitted by officers, dispatchers, or supervisors to acknowledge instructions, updates, or status changes.
Common uses of 10-4 include:
- Confirming receipt of assignments or directions
- Acknowledging status updates or information broadcasts
- Indicating understanding without interrupting radio flow
Unlike 10-8, which indicates that a unit is available or in service, 10-4 simply confirms understanding and does not imply any change in operational status.
Variations And Interpretation
Although 10-4 is widely understood as “acknowledgment,” its nuance is important. The code confirms that a message was received and understood, but it does not necessarily mean agreement, approval, or immediate action.
This distinction is especially important in complex or high-risk operations, where acknowledgment must be clearly separated from execution or compliance.
Plain-Language Alternatives
Agencies that use plain-language communication often replace 10-4 with brief acknowledgments such as:
- "Copy."
- "Received."
- "Understood."
These alternatives serve the same function while reducing ambiguity during multi-agency or inter-jurisdictional responses.
Modern Relevance
Despite a gradual shift away from coded radio language, 10-4 remains deeply embedded in radio culture and is widely recognized even outside public-safety contexts. Its simplicity and clarity continue to make it useful in both formal and informal communication.
Whether used as a code or spoken plainly, the purpose of 10-4 remains unchanged: to confirm that a message has been successfully received and understood.
Related 10-Codes
Codes commonly referenced alongside 10-4 include 10-1 (signal weak), 10-2 (signal good), 10-3 (stop transmitting), and 10-8 (in service). Together, these codes form a compact system for managing radio clarity, acknowledgment, and operational flow.