Understanding Police Radio Codes in the U.S.

Police and other public safety officers often speak in numeric shorthand over the radio rather than using full sentences. These police radio codes – most famously the “10‑codes” – are brevity signals that stand for common phrases or status messages. For example, instead of saying “I have arrived on scene,” an officer might say “10‑97.” Such codes were designed to speed communication, reduce radio chatter, and (to some extent) obscure sensitive information from casual listeners. In fact, police 10‑codes are officially known as the APCO “Project 14” Aural Brevity Code. By condensing routine information into short numeric phrases, these codes helped early radio users communicate efficiently. For instance, “10‑4” universally means “acknowledged” or “okay,” and “10‑9” means “repeat that”. (A long list of other common codes is given below.)

Police officers often use numeric radio codes to communicate quickly and clearly during operations.

Historically, police codes evolved alongside two-way radio technology. In the 1920s–1930s, one-way and then two-way mobile radios revolutionized policing. By the 1940s radio channels were crowded, and there was a strong desire to keep routine messages brief and somewhat private. Illinois State Police communications director Charles “Charlie” Hopper is credited with devising the first police 10‑code system around 1937. Hopper’s goal was a uniform shorthand that all officers could use for faster communication. Over the decades, these codes spread nationwide. The Association of Public-Safety Communications Officials (APCO) published a standardized set of 10‑signals in the 1940s and expanded them in 1974. In practice, however, most agencies soon adapted the system to local needs, so that codes vary widely from place to place (more on that below).

For much of the 20th century, police codes were almost universal in U.S. law enforcement radio traffic. They even made their way into pop culture – think of the old TV cop show Adam-12 and rappers mentioning “187” (California’s homicide code) or “10‑4” on radio. But beginning in the 2000s, officials at the federal level began urging a move toward plain language (everyday English) on emergency radios. Large multi-agency incidents – most famously the 9/11 attacks and Hurricane Katrina – exposed how different code sets could cause deadly confusion among responding units. For example, the Department of Homeland Security (DHS) and FEMA reported that after Katrina relief workers struggled with incompatible radio codes, and in 2006 the federal government formally recommended phasing out 10‑codes in favor of common language. Today, many departments still use 10‑codes internally, but interoperability standards (under NIMS and other programs) strongly push plain English when multiple agencies operate together. (The sections below explain these developments in detail.)

What Are Police Radio Codes?

Police radio codes are brevity codes – short numeric signals meaning specific phrases – used by law enforcement and other first responders. The most famous are the “10‑codes,” where each code starts with “10” and a two-digit number. For example: “10‑20” means “What is your location?” or “Location,” while “10‑97” means “Arrived on scene”. There are also signal codes (which may or may not use “10” as a prefix) and penal codes (often just citing the relevant law section, e.g. “187” for murder in California).

Codes exist mainly for brevity and clarity on the radio. In high-stress or fast-moving situations, officers can convey routine information with just a few digits. A training manual notes that code signals are used “whenever possible” to maintain brevity and to make it harder for unauthorized listeners to monitor police operations. In practice, this means fewer radio transmissions and less chance of misunderstanding over static-prone channels. For example, rather than saying “Suspect is in custody,” an officer might say “10‑6 out of car, suspect in custody” using a coded form.

As one professional guide puts it, 10‑codes “ensure clarity, especially in high-pressure situations, by reducing the risk of miscommunication”. In short, police codes are a specialized radio language developed to save time and standardize messages in police work. (Of course, different code systems have emerged as well – see below.) Importantly, these codes were never meant to be secret from the public (as a 2005 article notes, “codes are no secret”); rather they are tools for inter-officer communication.

History of Police Codes

The roots of police radio codes go back to the early days of radio. In the 1920s and 1930s, cities installed one-way police radio broadcasts, and by the late 1930s two-way radios came into use. This revolutionized communication but quickly crowded available radio channels. Dispatchers and officers therefore needed ways to communicate briefly while protecting sensitive information (since any listener could tune in).

• 1930s – Chicago and Illinois: In 1937 communications expert Charles “Charlie” Hopper, of the Illinois State Police, created a set of numeric signals so officers could convey common messages faster. This system spread throughout Illinois and beyond, allowing, for example, each digit’s change to signal a different outcome (such as the last number indicating various message types).
• 1940s-1970s – APCO Standardization: The Association of Public-Safety Communications Officials (APCO) – then a new organization of dispatchers and radio experts – published a standard 10-code table (Project 14) in 1940. This “10-signal” code list was later expanded in 1974. APCO’s versions helped some uniformity: for example, 10-4 came to mean “affirmative/OK” in almost all APCO-based code lists. (APCO also maintained a special “police” phonetic alphabet parallel to the radio alphabet to spell things succinctly.)
• 1980s-2000s – Local Adaptations: In practice, as jurisdictions grew, many departments customized codes. Some agencies combined 10-codes with local “signal” codes or even penal-law codes. For instance, California’s highway patrol famously uses penal code numbers (“187” for murder, “459” for burglary, “415” for a disturbance, etc.) instead of 10-codes. Others might use “Signal 100” to signal a statewide emergency, or have unique meanings for codes like 10‑33 (e.g. “officer needs help” vs “weather report”). Because there was no centralized authority, variations proliferated.

These local differences eventually had consequences. On Jan. 13, 1982, an Air Florida 737 crashed in Washington DC at the same time as a subway crash and blizzard. Nineteen agencies responded, each with its own code system; cross-communication broke down, delaying the rescue effort. Similarly, during the Sept. 11, 2001 terrorist attacks and Hurricane Katrina (2005), responding officers from different jurisdictions could not easily understand one another’s radio codes. These crises underscored that in multi-agency disasters, incompatible codes can hinder life-saving coordination.

By 2006, the U.S. Department of Homeland Security – incorporating FEMA and the NIMS (National Incident Management System) framework – formally recommended discontinuing 10-codes in favor of plain English. That recommendation did not outlaw codes for local use, but it marked a strong national shift. (Indeed, FEMA’s NIMS Integration Center subsequently required plain language for all multi-agency incidents, tying it to federal grant funding.)

Different Radio Code Systems

In the U.S. today, you’ll still find a mix of radio code systems:

• 10‑Codes (Ten-Signals): The classic system where messages start with “10-”. Though often associated with police, 10-codes are used by fire, EMS, and even citizen’s band (CB) radio aficionados. Many departments have their own slight versions, but APCO’s official 10-code list is widely known.
• Signal Codes: Some agencies (especially in the Midwest or certain states) use “Signal” followed by a number. For example, Indiana’s sheriff codes include “Signal 100” to mean an emergency where all units must hold radio traffic. (Similarly, many departments use non-“10” signals like “10‑33” or “code 33” to mean things like “emergency traffic only” or “officer down.” In one training manual, “code 0-45 through 10-48” even specify how many units to dispatch to a large incident.)
• Penal or Incident Codes: Some places use numeric codes derived from state law sections. The best-known example is California: “187” means murder (from CA Penal Code), “211” means robbery, and so on. Officers there might report “390 on Main St.” to mean a hit-and-run (CA Vehicle Code 390), etc. Other states may have similar local code numbers.
• Plain Language: Increasingly, agencies simply use common phrases in plain English on the radio, especially when communicating with other jurisdictions. Under NIMS interoperability guidelines, responders are encouraged to say things like “man with gun” instead of “417,” or “officer down, we need EMS” instead of a coded message. This practice has become the norm during large-scale disasters and multi-agency operations.

Each system has its reasons. 10-codes were invented to be short and discreet, while signal codes often evolved in parallel. Penal codes leverage existing legal numbers. But the downside is obvious: a code like 10-33 might mean “officer needs help” in one town but “speed check” in another. As Police1 writes, “depending on where you’re from, a 10-33 could either mean spotting a traffic backup, or seeing a downed officer” – hardly interchangeable.

Therefore, some departments have moved toward uniformity. For example, APCO International (which produces radio communications standards) now advocates replacing all police 10-codes with plain language to ensure clarity. Likewise, the U.S. DHS quietly “asked police agencies to voluntarily make the switch” to plain talk after 9/11 and Katrina. But note: many agencies still keep at least some local codes in use. As one communication specialist notes, tradition and habit make change slow – “tradition is the biggest roadblock to progress” in law enforcement radio.

Unlike a fixed national code list, U.S. police agencies often maintain their own radio codes. For example, some state units use “signal” codes (as on these shirts) or penal‐code numbers instead of APCO’s 10‑codes.

Common 10-Codes and Meanings

Below are some frequently used 10‑codes, based on a standard APCO-type list. (Remember that meanings can vary by region, so this is a representative sample.)

• 10-4: Affirmative / Acknowledgment (“Message received”).
• 10-20: Location (“What’s your 10-20?” = “What is your location?”).
• 10-97: Arrived on scene.
• 10-9: Repeat last transmission.
• 10-7: Out of service (end of shift / unavailable).
• 10-8: In service (available).
• 10-10: Negative / No.
• 10-22: Disregard / Cancel last (scrub the previous message).
• 10-26: Detaining a subject.
• 10-27: Drivers license check.
• 10-28: Vehicle registration check.
• 10-31: Crime in progress.
• 10-32: Person with a gun.
• 10-33: Emergency, all units standby / “We have emergency traffic only”.
• 10-50: Traffic accident.
• 10-52: Ambulance needed.
• 10-97: Arrived on scene (often called out to indicate arrival).

Each item above comes from a standard list of 10‑codes. A full APCO-style code list runs from 10-0 (“use caution”) up through 10-99 and beyond, but the most common numbers deal with routine dispatch functions like the examples above. (For instance, 10-1 = “signal weak,” 10-3 = “stop transmitting,” 10-23 = “stand by,” etc..) Knowing these codes helps officers quickly acknowledge orders, request information, and report status without lengthy speech.

Plain Language in Communications

In recent years, police and public safety agencies have been shifting toward plain language radio communications – that is, using ordinary English phrases rather than numeric codes. The National Incident Management System (NIMS) strongly encourages plain talk for multi-agency operations. In fact, as of 2006 a NIMS Alert requires plain English for all major multi-jurisdiction emergencies; beginning in FY 2006, federal preparedness grants were even contingent on using plain language in mutual-aid incidents. Put simply, if your department wants federal disaster-response funding, it is expected to drop the codes during joint operations.

There are good reasons for this. Plain language eliminates ambiguity between agencies and improves interoperability. As one FEMA FAQ puts it, the goal is “to avoid confusion and misinterpretation among different agencies” and to comply with federal mandates. By saying “shots fired in the lobby” instead of a numeric code, officers ensure that everyone on the channel – police, fire, EMS, emergency managers – immediately understands the situation. Many large-city police departments (e.g. Chattanooga, TN) adopted plain talk after finding their radios clogged with incompatible codes during tornado and flood responses – “it was a nightmare,” according to one chief.

The benefits of plain language include: clearer communication, easier coordination with other responders, and fewer misunderstandings in a crisis. For example, when a Missouri highway patrol dispatcher switched from coded language to plain English during a 2005 emergency, all units understood “trooper in ditch, ordering ambulance” and responded swiftly – likely saving the wounded officer’s life. By contrast, a radio call laden with local code terms might be misinterpreted by arriving mutual-aid crews.

However, switching to plain talk is not without challenges. Many officers worry about officer safety and privacy: coded phrases can obscure exactly what’s happening, and plain English might broadcast a suspect’s actions to bystanders or the media. There are also practical hurdles: agencies must update computer dispatch systems and retrain personnel, which takes time and money. In fact, some chiefs argue that having no codes at all could actually degrade response if officers instinctively fall back on codes under stress. And plain language is still not universally taught in academies, so many newcomers learn whatever system their agency currently uses.

Nevertheless, national policy and experience are driving the change. DHS and FEMA circulated alerts calling for plain English, and public-safety organizations (like APCO International, the International Association of Fire Chiefs, and sheriffs’ associations) have endorsed “minimiz[ing] or eliminat[ing] coded substitutions” on emergency radios. By the late 2010s, departments large and small were voluntarily phasing out 10‑codes during major incidents. The trend is clear: while codes may persist in internal use, everyday language is the future of inter-agency communication.

Variations by State and Agency

There is no single national standard for police codes. Each state and department often maintains its own list. As a result, the same code can have wildly different meanings across jurisdictions. For example, in one agency “10-13” might mean “officer needs assistance,” while in another it simply means “weather report”. In theory, APCO’s list could unify codes, but enforcement is voluntary. Many areas have adapted codes to local culture – a small town might add codes for livestock or deer, whereas a big city might use dozens of codes for specific crimes. After all, as one sheriff’s foundation article notes, differences arose due to “local adaptations,” “state and regional differences,” and even specialized agency needs. In short, without a centralized authority, variety grew naturally.

Some examples of regional differences:

• California: State law codes dominate. Officers will say “415” (disturbance) or “459” (burglary) instead of a 10-code. (“416” even means a person with a gun, paralleling 10-32 elsewhere.) Radio lore is so entrenched that California’s penal codes are part of everyday speech (hence songs and cop shows using “187” for homicide).
• “Signal” codes (Midwest, etc.): Some departments (e.g. parts of Indiana, Michigan, Oklahoma) use “Signal 1, Signal 2, …, Signal 100” as their standard. For instance, in one Indiana sheriff’s department “Signal 100” means an emergency where all units hold routine radio traffic. (Oklahoma’s highway patrol similarly uses Code 100 for statewide emergencies.) Other signals like “Code 12” or “10‑33” may be local shortcuts.
• APCO 10-codes with tweaks: Many agencies officially use APCO’s 10-code system but make small changes. LAPD and NYPD, for example, historically used slightly different phonetic alphabets and might have their own definitions for a few 10-codes. Police1 notes that even phonetic terms vary by city. In practice, an officer relocating might need a “cheat sheet” of that department’s specific codes.

Because of this patchwork, major emergencies almost always default to plain language by policy. Even so, smaller local incidents and daily patrols often still rely on whichever code set the officers grew up with. This means an “insider language” survives alongside efforts at standardization.

Training and Standardization Efforts

Police radio codes are typically learned on the job and in training. New recruits usually memorize their agency’s codes during the academy or field training. Dispatch training manuals and field training officers emphasize the why as much as the what. For instance, one U.S. Justice Dept. communications manual instructs recruits that code signals maintain brevity and “make it difficult for unauthorized persons to monitor police operations”. In other words, officers are taught that codes save airtime and offer a layer of confidentiality. The same materials often include an official list of department-specific codes and the phonetic alphabet, and cadets must drill these until they become second nature.

On the standardization front, APCO International remains a leading voice. They still publish model radio code lists and offer communications training courses (in call-handling and dispatch). Many state and regional bodies also compile recommended code lists. However, in practice each department’s policies prevail. The growing emphasis from NIMS/ICS (the Incident Command System used in multi-agency responses) is to train officers in plain language for mutual-aid events. In fact, NIMS requires plain English only for multi-agency incidents, but it recommends using plain talk even day-to-day. Some states (like Minnesota and Louisiana) have even included plain-language drill exercises in their emergency plans to accustom responders to it.

In summary, there is more formal support today for communication training that minimizes codes. A 2007 SAFECOM report noted that federal grant rules “became contingent on the use of plain language” when responders from different agencies work together. Many police academies now address the plain vs. code issue directly, encouraging officers to use clear phrases. At the same time, basic radio etiquette – discipline in speaking, repeating critical information, etc. – remains universal. Efficient radio skills (code or not) continue to be a fundamental part of police communications training.

Examples from the Field

Real incidents show how radio codes (or lack thereof) can dramatically impact outcomes:

• Missouri Trooper Rescue (2005): NPR reported that a State Trooper was found shot and lying in a ditch in Independence, MO. A passing patrol officer radioed dispatch, who then broke the news to troopers in plain language: “They have a trooper in the ditch, they are ordering the ambulance, they are also trying to get Life Flight.” Crucially, the dispatcher did not use any 10-codes (because in Missouri the relevant codes didn’t match). As a result, every trooper in a 50-mile radius understood immediately and raced to the scene. The wounded trooper survived and the suspect was caught. This case became a famous example of plain talk potentially saving a life.
• Post-9/11 and Katrina Responses: During the September 11 attacks and Hurricane Katrina, thousands of officers from different jurisdictions converged on New York, DC, and New Orleans. The widespread use of assorted local codes led to “utter confusion” on the radio. In the aftermath, the Department of Homeland Security explicitly asked agencies to switch to plain English for such multi-unit crises. Many departments (e.g. Midwest City OK Police Department) took that advice; their chiefs later reported that abolishing 10-codes solved major communication headaches in storms and mass-casualty events.
• Daily Policing: Even outside disasters, codes remain embedded in routine work. A Chicago blog notes that while “10-4” (affirmative) is recognized nationwide, police radio scanners reveal how volatile meanings can be. For instance, one department’s “10-33” might mean “traffic backup,” while another’s means “officer needs help”. In practice, this means experienced officers usually learn (or keep with them) their own department’s “cheat sheet” of codes. Some agencies have developed their own manuals or intranet pages listing all active codes and signals for trainees and veterans alike.
• Pop Culture and Public Awareness: Police codes have seeped into popular culture. TV shows like Adam-12 and Dragnet frequently used 10-codes on air, and phrases like “What’s your 20?” or “10-4” entered the general lexicon. Contemporary media still reference them: rappers drop “187” for homicide, for example. This public familiarity can be a double-edged sword – it means that codes aren’t truly secret (as one chief wryly observed, “the public pretty much knows” them), but it also means most people at least recognize basic code sounds.

Conclusion

In summary, U.S. police radio codes are a legacy shorthand system born of early radio needs. They have allowed law enforcement to communicate common messages in a compressed form, improving speed and consistency on dispatch channels. Over decades, many variations of the 10‑code and related signals emerged, reflecting local priorities and culture. However, the late 20th and early 21st centuries have seen a major trend toward plain-language communication, driven by federal interoperability requirements and hard-learned lessons from large-scale emergencies.

Today’s officers often juggle both worlds. On one hand, they learn their agency’s traditional codes (in academy classes, briefing rooms, and field training) for quick internal use. On the other, they must be ready to drop the codes and “speak traffic” in straightforward English when coordinating across jurisdictions. This dual practice aims to capture the best of both: brevity and privacy when handling routine work, without sacrificing clarity and unity during crises. As one communications guide concludes, plain language is “the future of law enforcement communication,” but its success “requires cultural change within the organization”. In other words, even as the radio towers and dispatch consoles change little, the way officers talk into the microphone is evolving – and it will continue to do so for the sake of public safety.