|This article does not cite any references or sources. (December 2008)|
Police radio is a communications radio system used by law enforcement agencies all over the world.
Many such systems are encrypted to prevent eavesdroppers from listening in.
The vast majority of economically developed countries police services have access to such equipment; also, in most countries, police cars have sets which are designed to receive calls from the control room, and respond. Also, small personal radios exist that allow each officer to carry one easily, as well as a large central room at the Police station which directs personnel to the location of emergency incidents. Portable police radios first appeared within the British police in 1969.
In Norway, it is legal for private citizens to listen to the police radio, There are even streams available online.
It's legal under the Wireless Telegraphy Act 1949 to listen to police radio in the UK, it being impossible to ban such reception. But it is illegal to "act upon any information" picked up from those transmissions. For example, a journalist cannot go to a crime scene to cover the case if he heard a message on police radio. The move from open analogue to the encrypted digital Airwave system in the UK has made it practically impossible to just listen in to police radio.
Due to recent outbreaks of system down times, the Police and Fire services have emergency back-up radio broadcasting on analogue for threats against the main control centre. The Ambulance Service however has mobile phone systems in place until the system has been updated.[verification needed]
U.S. state patrols, county sheriffs' offices, and municipal police departments often run their own systems in parallel, presenting interoperability problems. The FCC assigns licenses to these entities in the public safety (PP and PX) allotments of the spectrum. These include allocations in the lower portion of the VHF spectrum (around 39 - 45 MHz), highly susceptible to "skip" interference but still used by state highway patrols; the VHF "hi-band", from 150 to 160 MHz; and various UHF bands. Many systems still use conventional FM transmissions for most traffic; others are trunked analog or digital systems. Recently, there has been a move towards digital trunked systems, especially those based around the public-safety standard Project 25 format set by the Association of Public-Safety Communications Officials-International. A minority of other police radio systems, the largest examples being the Milwaukee Police Department and Pennsylvania State Police use the incompatible OpenSky format. TETRA, the standard in many European countries as well as other places in the world, is virtually unused in the United States.
Recently, some states have began to operate statewide radio networks with varying levels of participation from police on the county and city levels. Some of them are:
- Illinois: StarCom21
- Louisiana: LWIN Louisiana Wireless Information Network
- Michigan: MPSCS Michigan Public Safety Communications System
- Minnesota: ARMER 
- Montana: Montana Statewide Interoperable Public Safety Radio System 
- North Carolina: VIPER 
- Ohio: MARCS - Multi-agency communications system
- Wisconsin: WISCOM 
It is generally not illegal in the United States to listen to unencrypted police communications. However some states prohibit such listening within vehicles.