Listen to a police scanner for more than a few minutes and you’ll hear a jumble of numbers: “10-4,” “11-99,” “we’ve got a 459 in progress.” They sound like one system, but they’re actually three different families of code, each with its own history, purpose, and territory. Confusing them is one of the most common mistakes people make when learning to follow police radio. This article untangles the three — 10-codes, 11-codes, and penal codes — and explains what each one is for and where you’ll hear it.
The short version: 10-codes are general radio shorthand used across the country, 11-codes are a mostly-California set focused on traffic and roadway incidents, and penal codes are actual criminal statute numbers spoken aloud to name specific crimes. They often appear together, especially in California, which is why they’re so easily mixed up.
10-Codes: The National Radio Shorthand
Ten-codes are the ones most people picture when they think of police radio. Each is the word “ten” followed by a number — 10-4, 10-20, 10-50 — and together they cover the everyday business of radio communication: acknowledging a message, giving a location, reporting a status, flagging a traffic accident.
They were created in the late 1930s by Charles Hopper of the Illinois State Police and formalised by the Association of Public-Safety Communications Officials (APCO). The “ten” prefix originally served a technical purpose, giving early radio transmitters a split second to reach full power before the meaningful number was spoken. The system spread nationwide and became the default radio shorthand for American law enforcement.
The catch, which runs through everything about police codes, is that ten-codes are not truly standardised. APCO recommended a list, but adoption was voluntary, and departments modified the codes to suit local needs. So while some ten-codes are nearly universal — 10-4 for “acknowledged” being the prime example — others vary sharply between jurisdictions. Here’s a sample of common ten-codes to show their range:
| Code | Common meaning |
|---|---|
| 10-4 | Acknowledged / message received |
| 10-7 | Out of service |
| 10-8 | In service / available |
| 10-20 | Location |
| 10-32 | Person with a gun (varies) |
| 10-50 | Traffic accident (varies) |
Ten-codes are the foundation, the layer you’ll hear on the most channels in the most states. For the full history and list, see our US 10-codes guide, and for the broader context, our overview of US police codes.
11-Codes: California’s Traffic-Focused Set
The 11-codes are where people start to get confused, because they look just like ten-codes — “eleven” followed by a number — but they’re a distinct family with a different focus and a much narrower geography. They’re associated above all with the California Highway Patrol (CHP) and are used by many California agencies alongside the standard ten-codes.
The defining feature of the 11-codes is their concentration on traffic and roadway incidents, which makes sense given their Highway Patrol origins. Where ten-codes handle general communication, the 11-codes drill into the specifics of collisions, road hazards, and vehicle-related situations. A cluster of them covers traffic accidents by severity, which is exactly the kind of fine distinction a highway agency needs:
| Code | Meaning |
|---|---|
| 11-80 | Traffic accident — major injury |
| 11-81 | Traffic accident — minor injury |
| 11-82 | Traffic accident — no injury |
| 11-83 | Traffic accident — no details |
| 11-84 | Direct traffic |
| 11-85 | Tow truck required |
| 11-98 | Meet the officer |
| 11-99 | Officer needs help (emergency) |
That 11-99 at the bottom is the most famous of the set — the CHP’s call for urgent officer assistance, its equivalent of the emergency that other agencies signal with entirely different numbers. In California, then, a single channel might carry ten-codes for general communication and 11-codes for the roadway specifics, side by side. To someone unaware that these are two families, it just sounds like a long, inconsistent list of numbers. Knowing that “10-” is general shorthand and “11-” is the traffic-focused California layer makes the whole stream far easier to parse. For how these fit within the national catalogue, our US police code category lays it out.
Penal Codes: Speaking the Statute Number
The third family is different in kind, not just in numbering. Penal codes are actual section numbers from the criminal code, spoken aloud to name a specific crime. They aren’t radio shorthand invented for communication; they’re references to the law itself, borrowed onto the radio because they map cleanly onto the crime and, eventually, the charge.
This practice is strongly associated with California, where officers routinely say California Penal Code section numbers on the air. The most famous is 187, the section defining homicide, which has spread so far into popular culture that many people recognise it as slang for murder without knowing it’s a statute. Other common ones:
| Code | Crime (California Penal Code) |
|---|---|
| 187 | Homicide/murder |
| 207 | Kidnapping |
| 211 | Robbery |
| 415 | Disturbing the peace |
| 459 | Burglary |
| 487 | Grand theft |
The key difference between ten-codes and 11-codes is the source. A ten-code was designed as a communication tool; a penal code number is a legal citation that officers happen to speak over the radio. When you hear “459 in progress,” the officer is naming the burglary statute directly. This is why California radio can sound so number-dense — a serious call might combine a response code, an 11-code for the roadway detail, and a penal code for the crime, all in one transmission. It’s also why penal-code usage varies by state: California defines burglary at section 459, but another state’s burglary statute carries a completely different number, so “459” is meaningful in California and meaningless as a code elsewhere.
How They Work Together — and Why They Get Confused
The reason these three families are so often muddled is that in California they genuinely coexist on the same channels, layered on top of one another. A single incident might be described with all three at once:
- A 10-code sets the communication and status (“10-97” on scene).
- An 11-code captures a roadway-specific (“11-85” tow truck required).
- A penal code names the crime (“211” robbery).
- On top of these sits the Code system (Code 3 for an emergency response, Code 4 for situation under control), which is yet another distinct family governing how urgently an officer responds.
To an untrained ear, that’s an undifferentiated wall of numbers. But each layer answers a different question. The response Code says how fast. The 10-code says what’s my status and communication. The 11-code says what’s the roadway situation. The penal code says what crime. Once you sort each number into its family, the wall resolves into a precise, efficient description of an incident. This layering is a California specialty; a department in another state might use only ten-codes, or ten-codes plus local signals, and skip the 11-codes and spoken penal codes entirely.
Which One Will You Actually Hear?
Where you’re listening determines which families are in play. In much of the country, you’ll mostly hear ten-codes, sometimes mixed with plain language and, in the Southeast, with signal codes instead. In California and some neighbouring western areas, you’ll hear the full stack: ten-codes, 11-codes, penal codes, and the Code response system together. Agencies that have moved toward plain language will use fewer codes of any kind, especially for complex or multi-agency situations, following the federal guidance that emerged after communication breakdowns during Hurricane Katrina exposed the dangers of inconsistent codes.
Countries outside the US generally use none of these families. The United Kingdom, for instance, never adopted American-style numeric codes and communicates in plain language, as our UK police codes guide explains — a useful reminder that this three-family system is a particular American development, not a universal feature of policing.
A Simple Way to Keep Them Straight
If you remember nothing else, remember what each family is for. Ten-codes are general-purpose radio shorthand used broadly across the country. Eleven-codes are the California traffic-and-roadway set, recognisable by their focus on collisions and vehicles and topped by the famous 11-99. Penal codes aren’t communication codes at all — they’re criminal statute numbers spoken aloud, jurisdiction-specific, with 187 the best-known example. And the Code response system, easy to lump in with the rest, is a separate fourth family that governs urgency rather than content.
Sorting numbers into those buckets is the single skill that turns a confusing scanner feed into a readable one. The families were never meant to be one system, and treating them as one is what makes police radio sound impenetrable. Treat them as what they are — distinct tools that happen to share the air — and the logic behind the numbers comes into focus.
Using Police Code to Explore Further
Police Code is a global police code explorer built to make exactly these distinctions clear. Instead of facing an undifferentiated list of numbers, you can search one organised database that separates ten-codes, 11-codes, penal codes, and response codes, shows how each is used across agencies and countries, and points to the references behind them. It’s free to browse and built for scanner listeners, journalists, writers, and anyone learning to read police radio. When a single California transmission stacks four families of code in one breath, having them sorted and explained in one place is the fastest way to make sense of it.