Police code Signal 9 does not have a single meaning. It changes from agency to agency: in one sheriff’s office it refers to a stolen license plate, in another it means “disregard” (cancel a previous instruction), and in others it has been used for a bomb threat or a person in mental health crisis. The only reliable way to know what Signal 9 means on a particular radio channel is to check the codebook of the department using it.
Documented Meanings of Signal 9
Signal codes are built internally by each agency, so the same number can refer to unrelated situations depending on who is speaking. Documented uses of Signal 9 include:
- A stolen license plate, used by at least one county sheriff’s office.
- “Disregard,” meaning cancel a previous dispatch, used by other departments.
- A bomb threat, in some agencies.
- A person experiencing a mental health crisis, in others.
“Code 9,” which uses a different prefix with the same number, has been documented as a roadblock instruction in yet another system. These are not rare edge cases. Two neighboring agencies can use Signal 9 for entirely different call types, and neither is wrong, because no governing standard exists. Anyone hearing Signal 9 on a scanner or in a news report who assumes it means one thing everywhere will almost certainly misunderstand it somewhere.
Why the Same Code Means Different Things
Law enforcement radio shorthand generally falls into two families: ten-codes and signal codes. Ten-codes are the more widely recognized system, using a “10-” prefix followed by a number. “10-4” for acknowledgment and “10-7” for out of service are familiar even to people who have never touched a scanner.
Signal codes use the word “Signal” followed by a number and tend to be even less standardized than ten-codes. Where ten-codes at least started from a common framework before departments modified them, signal codes were often built from scratch by individual agencies. The result is a patchwork where the same signal number carries a different meaning almost everywhere it is used.
Even ten-codes drifted over the decades. Departments added their own variations, dropped codes they did not need, and repurposed numbers for local priorities. When major incidents required agencies from different regions to work together, officers discovered that their codes did not line up.
That mismatch is part of what pushed the federal government toward plain language for multi-agency responses under the National Incident Management System, with preparedness grant funding tied to the requirement since fiscal year 2006. The policy strongly encourages plain language for routine communication so responders practice the same terminology they will need during large-scale emergencies, but it does not ban codes for everyday internal use.1FEMA. NIMS Alert – Plain Language Many agencies still use codes internally and switch to plain language when coordinating with outside departments.
How to Find What Signal 9 Means in Your Area
Start with the agency’s official website. Many police departments, sheriff’s offices, and fire departments publish their code lists online, sometimes under a “community resources” or “transparency” section. A search for the department name plus “radio codes” or “signal codes” often turns one up.
When the codes are not posted online, you can submit a public records request directly to the agency. The federal Freedom of Information Act covers only federal agencies, not local police departments or sheriff’s offices.2FOIA.gov. Freedom of Information Act For local and state agencies, every state has its own public records law granting residents the right to inspect government documents. The name varies by state (Open Records Act, Public Records Law, and others), but the principle is the same: you can request internal documents such as codebooks. Be specific about the document you want. Expect an initial response within roughly five to ten business days in most states, though timelines vary.
Online scanner communities and hobbyist websites sometimes compile code lists for various departments. These can be a useful starting point, but treat them as unofficial. Codes change, departments update their systems, and volunteer-maintained lists do not always keep pace.
Encryption Is Making Signal Codes Harder to Hear
Even if you know every code your local department uses, you may not be able to listen in. Denver, New York City, Chicago, San Francisco, and dozens of smaller jurisdictions have switched to encrypted radio systems in recent years, converting transmissions into signals that consumer scanners cannot decode. Supporters say encryption protects officer safety and prevents suspects from monitoring police movements. Critics say it removes a layer of public accountability that has existed for decades.
In encrypted jurisdictions, the codes become largely academic. You can learn what Signal 9 means where you live, but if the department has encrypted its radio traffic, you will not hear it being used in real time regardless.
Is Listening to a Scanner Legal?
Owning and using a police scanner is legal under federal law. Unencrypted police, fire, and EMS transmissions are fair game to listen to. Federal law prohibits intercepting certain private communications but specifically exempts radio transmissions made for public use, communications about ships, aircraft, or persons in distress, and amateur or citizens band radio.3Office of the Law Revision Counsel. 47 U.S. Code 605 – Unauthorized Publication or Use of Communications
State rules add restrictions. Some states prohibit using a scanner while driving, and using scanner information to help commit a crime is a separate offense in many states, with penalties ranging from misdemeanor fines to felony charges depending on the jurisdiction. Decoding encrypted or scrambled transmissions is also off-limits under the Electronic Communications Privacy Act of 1986, so attempting to bypass a department’s encryption crosses a legal line that simply listening to unencrypted traffic does not.