In APCO 10-codes, 10-4 means "Acknowledgment" or "Affirmative."
It is one of the most widely recognized 10-codes and is used to confirm that a message has been received and understood. For example, if a dispatcher gives an instruction or provides information, the responding officer can reply with 10-4 to indicate that the message was received:
- Dispatch: "Unit 5, respond to the scene at 123 Main Street."
- Officer: "10-4, en route."
This simple, efficient code helps facilitate clear communication, especially in high-stress or noisy environments.