Look up US police 10-codes (10-4, 10-20...) and CB/trucker meanings side by side
"Ten-codes" were created between 1937 and 1940 by Charles "Charlie" Hopper, communications director for the Illinois State Police, as part of the work of APCO (the Association of Police Communications Officials). The idea was practical: radios of the era ran on vacuum tubes powered by a small motor-generator (a dynamotor) that took a tenth to a quarter of a second to reach full power, so the first syllable of any transmission was often lost. Prefixing every phrase with "10-" gave the radio time to stabilize before the important part of the message, while also shortening traffic on shared channels. The list was expanded in 1974 (the so-called "APCO Project 14"), but there was never a central authority requiring every US agency to adopt the same numbers for the same meanings, over time, individual departments adjusted or reassigned codes to fit their own operational needs. In parallel, CB (Citizens Band) radio and trucker culture developed their own ten-code list, inspired by APCO's idea but diverging in practice: of the 56 codes curated in this table, 27 have a CB meaning that is verifiably different from the most commonly cited police use, 18 match in substance, and for 11 we could not find a reliably documented CB use at all. Outside the US, ten-codes are not part of any official public-safety protocol, for example, in Brazil most people's exposure to "10-4" or "code 10-20" comes from American movies, TV shows and video games, which is why "10-4" has become a near-universal piece of slang even among people who have no idea what most of the other ninety-odd codes mean.
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It's the code that comes closest to a universal consensus, both the police list and the CB list use "10-4" for acknowledgment/"understood". Even so, it isn't legally standardized; it's simply the most consistently used code, and the one that most escaped into everyday pop culture.
Unlike what movies and TV shows suggest, there is no single, official "ten-code" list in the United States. What each number means varies from department to department, from state to state, and it differs again between public-safety use (derived from APCO) and CB radio/trucker use. The same "10-50", for example, might mean "traffic accident" for one agency and something entirely different for another, and that lack of standardization has caused real confusion during joint, multi-agency operations. After Hurricane Katrina (2005), FEMA began discouraging the use of ten-codes in multi-agency relief operations, and the US Department of Homeland Security (DHS/SAFECOM) published its "Plain Language Guide" in 2008, recommending that public-safety agencies move radio communication toward plain language specifically to avoid this kind of misunderstanding during incidents involving multiple agencies, under National Incident Management System (NIMS) guidance. Treat the meanings in this table as the most commonly cited reference, not as a universal rule.
56 codes
| Code | Police use (APCO) | CB/trucker use | Comparison |
|---|---|---|---|
| Unable to copy — change location | Receiving poorly | Same | |
| Signal good | Receiving well | Same | |
| Stop transmitting | Stop transmitting | Same | |
| Acknowledgment (OK) | OK, message received | Same | |
| Relay | Relay message | Same | |
| Busy — unless urgent | Busy, stand by | Same | |
| Out of service | Out of service, leaving the air | Same | |
| In service | In service, subject to call | Same | |
| Repeat (say again) | Repeat message | Same | |
| Fight in progress | Transmission completed, standing by | Different | |
| Dog case | Talking too rapidly | Different | |
| Stand by (stop) | Visitors present | Different | |
| Weather / road report | Advise weather/road conditions | Same | |
| Civil disturbance | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Domestic problem | Make pickup at... | Different | |
| Meet complainant | Urgent business | Different | |
| Quickly | Anything for us? | Different | |
| Return to ___ | Nothing for you, return to base | Same | |
| Location | My location is.../What's your 20? | Same | |
| Call (___) by phone | Call by telephone | Same | |
| Disregard | Report in person to ___ | Different | |
| Arrived at scene | Stand by | Different | |
| Assignment completed | Completed last assignment | Same | |
| Report in person (meet) | Can you contact ___? | Different | |
| Detaining subject, expedite | Disregard last information | Different | |
| (Driver's) license information | I am moving to channel ___ | Different | |
| Vehicle registration information | Identify your station | Different | |
| Check for wanted | Time is up for contact | Different | |
| Unnecessary use of radio | Does not conform to FCC rules | Same | |
| Crime in progress | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Man with gun | I will give you a radio check | Different | |
| Emergency | Emergency traffic at this station | Same | |
| Riot | Trouble at this station, help needed | Different | |
| Major crime alert | Confidential information | Different | |
| Correct time | Correct time is ___ | Same | |
| (Investigate) suspicious vehicle | Wrecker needed at... | Different | |
| Stopping suspicious vehicle | Ambulance needed at... | Different | |
| Urgent — use light, siren | Your message delivered | Different | |
| Silent run — no light, siren | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Beginning tour of duty | Please tune to channel ___ | Different | |
| Ending tour of duty | Traffic accident at... | Different | |
| Information | Traffic tie-up at... | Different | |
| Permission to leave ___ for ___ | I have a message for you | Different | |
| Animal carcass at ___ | All units within range please report | Different | |
| Accident (fire/personal injury/property damage) | Break channel | Different | |
| Wrecker needed | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Ambulance needed | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Intoxicated driver | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Intoxicated pedestrian | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Fire alarm | Fire at ___ | Same | |
| En route ___ | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| ETA (estimated time of arrival) | Negative contact | Different | |
| Need assistance | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Notify coroner | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Bank alarm at ___ | We could not find a reliable, documented meaning for this number in CB/trucker radio use, we'd rather say so than make one up. | Not documented | |
| Wanted/stolen indicated | Mission completed, all units secure | Different |
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