The Signal 1 police code does not have one fixed meaning. Each law enforcement agency writes its own signal list, so the same two words can flag a drunk driver in one jurisdiction, an abandoned vehicle in another, and a call for backup in a third. If you heard “Signal 1” on a scanner or in a news report, the only reliable way to know what it meant is to know which department said it.
Common Meanings of Signal 1
A few documented uses show how far the definitions can stretch:
- Drunk driver. Several agencies, particularly in the Southeast, use Signal 1 for a driver suspected of operating under the influence of alcohol or drugs.
- Abandoned vehicle. At least one major metropolitan department assigns Signal 1 to an abandoned automobile, with no person involved at all.
- Officer needs assistance. Some departments build their signal tiers around backup requests, with Signal 1 as the lowest level and higher numbers signaling greater urgency or danger.
Those three uses have almost nothing in common. That is the point. Anyone who tells you Signal 1 universally means a specific thing is working from one department’s list and assuming it applies everywhere.
Why There Is No Standard Definition
Signal codes were never part of a national system. Individual departments created their own lists to label the situations they ran into most often, and those lists stayed local. A signal code in one county’s radio room reflects decisions made by that agency, not any outside authority.
This is where signal codes differ from ten-codes. Ten-codes came out of a deliberate standardization effort by the Association of Public-Safety Communications Officials (APCO), which proposed a common law enforcement code system in 1935 and developed its ten-code list between 1937 and 1940. The goal was a shared shorthand every agency could use. Even then, departments eventually modified ten-codes, added new ones, and reassigned meanings until the same ten-code could mean different things in neighboring counties.
If a standardized system drifted that far, it is no surprise that a never-standardized system like signal codes varies wildly from one agency to the next.
How to Find Out What Signal 1 Means in Your Area
Because the meaning is local, the answer lives with the local agency. A few practical options:
- Check the police department’s own website or public records. Some agencies publish their signal lists, particularly as part of training materials or public information releases.
- Ask the department’s public information officer directly. For a routine question about radio terminology, this is often the fastest route.
- Look at scanner community resources for your specific city or county. Local hobbyists frequently compile and share the signal lists in use on their regional frequencies.
Whatever source you use, confirm it reflects the agency whose transmission you heard. A signal list from the next county over may not match.
Plain Language Rules and Encryption Are Changing What You Hear
Two outside forces are reshaping how often you will encounter signal codes on the air at all.
The first is a federal push toward plain language. In 2006, the Federal Emergency Management Agency issued a directive through the National Incident Management System requiring plain language for multi-agency, multi-jurisdiction, and multi-discipline events like major disasters and large-scale exercises.1FEMA. NIMS Alert – Plain Language FEMA tied federal preparedness grant funding to compliance starting in fiscal year 2006, with payments contingent on agencies using plain language during incidents involving responders from other agencies or disciplines.2CISA. Plain Language Guide Frequently Asked Questions The rule does not abolish signal codes or ten-codes for everyday department communications, and agencies will not lose funding for using codes on routine internal calls. The practical result is a split: many departments still use their own codes day to day, then switch to plain English when working alongside outside agencies.
The second force is encryption. A growing number of police departments are encrypting their radio channels, which blocks scanner listening entirely regardless of whether the department uses codes or plain language. Encrypted channels can only be accessed by someone with the encryption key. Departments adopting encryption generally cite the exposure of sensitive personal information about victims and witnesses through modern scanner apps, and the risk that people in active criminal situations can monitor police response plans in real time. Multiple major departments across the country have announced or implemented encryption plans in 2025 and 2026. For anyone trying to decode what Signal 1 means on a given channel, encryption is the bigger obstacle than the code itself; if the channel is encrypted, you will not hear the signal in the first place.
The Short Version
Signal 1 is whatever the agency broadcasting it says it is. Three of the most frequently documented uses are drunk driver, abandoned vehicle, and a low-tier call for officer assistance, but none of those meanings is universal. Treat any definition you find as provisional until you confirm it against the specific department’s own signal list.