Police radio

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.
Portable radios.
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.
By country.
Germany.
In Germany, it is illegal for private citizens to listen to police radio, even if its unintentional. Individuals can be punished with up to two years in prison or heavily fined.
Norway.
In Norway, it was legal for private citizens to listen to the police radio, there were even streams available online. It is no longer possible to listen to the police radio, after Norway switched to "Nødnett".
United Kingdom.
Police radios were pioneered largely by Capt. Athelstan Popkess of Nottingham City Police in the early 1930's, with trials commencing in 1931, and the results published in a 1933–1934 series of articles. Interestingly these experiments concluded that wireless telegraphy was preferable to wireless telephony due to better signal, less chance of interception and being just as quick to send and receive by Morse proficient officers.
Popkess paired this use of police radios with his simultaneous development of increased use of police cars for patrol purposes stating that “There can be no real mobility unless [mechanization and communication] are closely related, and each is as efficient as we can make it”.
It is an offence under the Wireless Telegraphy Act 2006 to listen to police radio in the UK. 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.
United States.
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 150–160 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 begun to operate statewide radio networks with varying levels of participation from police on the county and city levels. Some of them are:
It is generally legal in the United States to listen to unencrypted police communications. However some states and municipalities prohibit carrying receivers within vehicles.