A police code is a brevity code, usually numerical or alphanumerical, used to transmit information between law enforcement over police radio systems in the United States. Examples of police codes include "10 codes" (such as 10-4 for "okay" or "acknowledged"—sometimes written X4 or X-4), signals, incident codes, response codes, or other status codes. These code types may be used in the same sentence to describe specific aspects of a situation.
Codes vary by state, county, and agency. It is rare to find two agencies with the same ten codes, signals, incident codes, or other status codes. While agencies with adjacent or overlapping jurisdictions often have similar codes, it is not uncommon to find differences even within one county or city. Different agencies can have codes dissimilar enough to make communication difficult. There are similarities among popular sets of 10-codes.[1]
The topic of standardized codes has been discussed in U.S. law enforcement circles, but there is no consensus on the issue. Some law enforcement agencies use “plain talk” or “plain codes” which replace codes with standard speech and terminology, albeit in a structured manner or format. Arguments against plain language include its lack of brevity, variability, and lack of secrecy which is often tactically advantageous or a safety issue when officer communications can be overheard by the civilian public.[2]