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.

The 256-bit variant of the Advanced Encryption Standard, providing the highest level of encryption security commonly used in public safety radio systems. The "256" refers to the key length in bits—longer keys are exponentially harder to crack. AES-256 is considered military-grade encryption and is virtually unbreakable with current technology.

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.

In DMR (Digital Mobile Radio) systems, a color code is a digital identifier (0-15) that distinguishes between different repeaters or networks operating on the same frequency. It functions similarly to CTCSS tones in analog systems, preventing interference between adjacent systems.

A connection created at the dispatch console that links two or more radio channels or talkgroups together, allowing users on different channels to communicate with each other as if they were on the same channel. Patches are essential for interoperability during multi-agency incidents.

In trunked radio systems, a dedicated frequency that carries digital data rather than voice. The control channel manages the system by assigning working frequencies to talkgroups, handling radio registration, and coordinating all system traffic. Scanners must first find the control channel to follow a trunked system.

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.

CTCSS (Continuous Tone-Coded Squelch System) and DCS (Digital-Coded Squelch) are methods of adding sub-audible tones or digital codes to radio transmissions. Receivers only open squelch when they detect the matching tone, preventing interference from other users on the same frequency. CTCSS uses analog tones (67-254.1 Hz), while DCS uses digital codes.

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 primary radio channel used by dispatchers to assign calls, broadcast BOLOs, provide information to officers, and coordinate routine police operations. Dispatch channels carry the bulk of police radio traffic and are the channels most commonly monitored by the public. In hybrid encryption systems, dispatch channels typically remain unencrypted.

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.

A standard interface defined in the P25 specification that allows different P25 radio systems to connect and communicate with each other. ISSI enables agencies with separate P25 networks to talk to each other without manual intervention, improving interoperability across jurisdictional boundaries.

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.

Designated radio frequencies or talkgroups specifically reserved for communication between different agencies during joint operations, emergencies, or when one agency assists another. Mutual aid channels are pre-programmed into radios so responders from different jurisdictions can immediately communicate without needing to know each other's regular frequencies.

In P25 digital radio systems, a 12-bit hexadecimal code (values $000-$FFF) that identifies which system or network a radio belongs to. NAC functions similarly to CTCSS tones in analog systems—radios will only unmute when they receive transmissions with a matching NAC. The default NAC for P25 is $293.

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.

Standard abbreviations in radio communications: RX means receive (listening), and TX means transmit (broadcasting). These terms are used in technical specifications and discussions. For example, a scanner is an RX-only device—it can receive but not transmit.

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.

A radio system architecture where multiple transmitter sites broadcast the same signal simultaneously on the same frequency. Simulcast systems provide seamless coverage across large geographic areas because the receiver picks up the strongest signal regardless of which site is transmitting. This is more complex than using different frequencies at each site but eliminates coverage gaps.

A circuit in a radio receiver that silences the audio output when no signal is present, eliminating the static and noise between transmissions. Users can adjust the squelch threshold to determine how strong a signal must be before the radio unmutes. Too high squelch may cut off weak signals; too low results in static breakthrough.

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. Each talkgroup can be individually configured for encryption or left open.

A digital radio technology that divides a single radio frequency into multiple time slots, allowing two or more simultaneous conversations on one frequency. P25 Phase II uses 2-slot TDMA to double channel capacity compared to Phase I. DMR also uses 2-slot TDMA.

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.

A radio system that uses multiple receivers at different locations to pick up transmissions from field units. A comparator evaluates the signal quality from each receiver site and "votes" for the best one, routing that audio to dispatch. This ensures clear reception regardless of where the transmitting unit is located.

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.