Glossary of Terms

A symmetric encryption algorithm used to secure digital radio communications. AES-256 is the most common encryption standard used in police radio systems. When enabled, AES renders radio transmissions unintelligible to anyone without the proper decryption key.

Traditional radio technology that transmits voice as continuous radio waves. Analog systems are inherently unencrypted and can be easily monitored with basic scanners. Most police departments have transitioned or are transitioning to digital systems.

Professional organization for public safety communications. APCO developed the Project 25 (P25) digital radio standard. APCO conferences and publications often discuss encryption policies.

An alert broadcast to officers to watch for a specific person, vehicle, or situation. BOLOs are typically broadcast on dispatch channels and include descriptions and reasons for the alert. Scanner listeners often hear BOLOs for missing persons, suspects, or stolen vehicles.

The largest online platform for streaming and archiving police scanner feeds. Volunteers operate scanner receivers and stream audio to the Broadcastify website and app. Archives are searchable and have been used for journalism and research.

Software system used by dispatchers to manage 911 calls, assign officers, and track incidents. CAD data is transmitted digitally (often encrypted) to officers' mobile data terminals. CAD systems contain more detailed information than voice radio.

A specific radio frequency or talkgroup designated for particular communications. Police departments typically have multiple channels for different purposes: dispatch, tactical operations, car-to-car, detective, etc.

Radio transmissions that are not encrypted and can be monitored by anyone with appropriate receiving equipment. "In the clear" means broadcasting without encryption.

A radio system where each channel has a dedicated frequency. Users manually select the channel they want to use. Simpler than trunked systems and easier to monitor with basic scanners.

Some jurisdictions with encrypted radios provide a delayed public feed of communications, typically 30-60 minutes behind real-time. Chicago, for example, offers a 30-minute delayed feed. Such delays eliminate the real-time value of scanner access for emergencies and breaking news.

Radio technology that converts voice to digital data for transmission. Digital systems offer clearer audio, better coverage, and the option for encryption. P25 is the most common digital standard for public safety. Digital transmissions can be either encrypted or unencrypted.

The centralized communication center (and the personnel operating it) that receives 911 calls, assigns officers to incidents, and coordinates police response. Dispatch communications are the core police radio traffic that the public has traditionally monitored via scanners.

The process of encoding radio transmissions so that only authorized receivers with the correct decryption key can understand them. Encrypted transmissions sound like static or noise to scanners without the key. Police departments use encryption to prevent public monitoring of radio communications.

The U.S. federal agency that regulates radio communications. The FCC allocates frequencies to public safety agencies and sets technical standards. FCC rules permit public monitoring of unencrypted radio transmissions.

An audio stream of scanner traffic, typically broadcast online via services like Broadcastify. Volunteers operate scanner receivers and stream the audio. In encrypted jurisdictions, police-provided delayed feeds may be the only option.

The specific radio wave used for transmission, measured in megahertz (MHz). Public safety radio frequencies are allocated by the FCC in specific bands (VHF, UHF, 700 MHz, 800 MHz). Each frequency can carry one conversation at a time in conventional systems.

When all police radio channels are encrypted with no public access. This is the most restrictive approach and eliminates all real-time public monitoring capability. Full encryption is what transparency advocates oppose.

A command or action to switch from unencrypted to encrypted communication. In hybrid systems, officers may "go secure" for sensitive tactical discussions and return to open channels afterward.

A radio configuration that maintains open (unencrypted) channels for routine dispatch while using encryption only for sensitive tactical operations. Hybrid systems preserve public access to routine police communications while protecting genuinely sensitive information. This is the approach advocated by transparency supporters.

The ability of different agencies' radio systems to communicate with each other. Interoperability is critical during multi-agency emergencies. Encryption can create interoperability problems when agencies use different encryption keys or systems.

FBI program that collects data on officer deaths and assaults, including circumstances and contributing factors. LEOKA data shows no documented cases of officers harmed due to public scanner access.

Computer terminals installed in police vehicles that display CAD information, allow officers to query databases, and send/receive text messages. MDT communications are typically encrypted and contain detailed personal information not broadcast on voice radio.

Programs offered by some police departments that provide credentialed journalists with access to encrypted radio communications in exchange for agreements not to broadcast certain information. These programs are controversial because they create tiered access and make journalists dependent on police cooperation.

The dominant manufacturer of police radio equipment, with approximately 70%+ market share in the U.S. Motorola (now Motorola Solutions) manufactures P25 radios, repeaters, and encryption systems. Critics note Motorola's financial interest in selling expensive encrypted systems.

A radio channel that is not encrypted and can be monitored by the public using scanner equipment. Open channels preserve the traditional public access to police communications.

The digital radio standard used by most public safety agencies in North America. P25 was developed to ensure interoperability between agencies. P25 radios can operate in either encrypted or unencrypted mode—encryption is a feature that can be enabled or disabled.

Radio channel used for routine patrol officer communications, including traffic stops, responding to calls, and officer-to-officer communication. Patrol channels carry the bulk of police radio traffic.

Information that can be used to identify a specific individual, such as names, addresses, Social Security numbers, or license plate numbers. Police often cite PII protection as a reason for encryption, though PII is typically transmitted via encrypted MDT rather than voice radio.

Comprehensive online database of radio frequencies and system information for public safety agencies. Radio Reference maintains data on which agencies are encrypted, which frequencies are in use, and historical information about radio system changes.

A device that receives radio signals and retransmits them at higher power, extending coverage area. Repeaters are typically located on towers or tall buildings. Police radio systems use networks of repeaters to provide coverage across their jurisdiction.

The world's largest professional organization for broadcast and digital journalists. RTDNA has identified police radio encryption as "the number one threat to journalism" and actively advocates against encryption.

A radio receiver capable of monitoring multiple frequencies, typically used to listen to police, fire, and EMS communications. Scanners range from handheld devices to desktop units to smartphone apps. Listening to unencrypted public safety radio is legal in all 50 states.

Radio technology where components traditionally implemented in hardware are instead implemented through software. SDR allows a computer with an inexpensive USB receiver to function as a sophisticated scanner. SDR cannot decrypt encrypted transmissions.

Numeric codes used in radio communication for brevity. Common examples include "10-4" (acknowledged), "10-20" (location), etc. Many departments have moved to plain language to improve interoperability and reduce confusion.

Radio channels designated for specific operations or units, separate from main dispatch. Tactical channels are often used for SWAT operations, surveillance, or special events. In hybrid systems, tactical channels may be encrypted while dispatch remains open.

In trunked radio systems, a virtual channel that groups users together. Unlike conventional channels with fixed frequencies, talkgroups are assigned frequencies dynamically by the system. Scanner users need to program talkgroup IDs to monitor specific units.

A radio system that dynamically assigns frequencies to users as needed, rather than dedicating specific frequencies to specific channels. Trunking makes more efficient use of radio spectrum. Monitoring trunked systems requires more sophisticated scanner equipment.

The principle that government operations, including policing, should be open to public observation. In the context of police radio, transparency means maintaining public access to dispatch communications so citizens can independently monitor police activities.

Radio frequencies in the 300-3000 MHz range. Many police departments operate on UHF frequencies (typically 450-470 MHz). UHF provides good building penetration but shorter range than VHF.

Radio transmissions that have not been encoded and can be received and understood by anyone with appropriate receiving equipment. Also called "clear" or "in the clear." This is the traditional state of police radio communications.

The system that sends emergency alerts to cell phones. WEA alerts include AMBER alerts, weather warnings, and other emergencies. WEA is often cited as an alternative to scanner access, but WEA alerts are typically delayed 15-30+ minutes compared to real-time scanner information.