A police scanner is a device which is used for scanning radio frequencies used by law enforcement. The scanner is capable of listening to multiple frequencies at once and playing transmissions as they are received. Police scanners are also known as radio scanners and most are capable of listening in on frequencies well beyond those utilized by law enforcement alone. Specialized models are also capable of decryption of encoded signals, although the legality of such models may be debatable in some regions of the world.
The police scanner has its origins in the 1970s, when police officers began using radio communications on a regular basis. The ability to listen to several frequencies at once allows people to hear numerous communications at the same time, which can be extremely useful for people like dispatchers. Most police scanners have a squelch feature so that the speaker only activates when the device finds audio to play. This ensures that people are not forced to listen to static while the scanner looks for frequencies which are broadcasting.
Other features can include lockout buttons which cause the scanner to skip frequencies the user is not interested in, as well as features which save or record frequencies. The features available depend on the model. Generally, the more features, the larger and more expensive a police scanner will be. Certain features may also not be legal in all areas and people should be careful when buying a scanner to confirm that it will not violate the law.
A police scanner can be set to check certain frequencies, to scan a range of frequencies, or to search for frequencies. Journalists use police scanners to get up to date information about the crime beat so that they can respond quickly to breaking news stories. Likewise, some hobbyists are interested in hearing law enforcement communications on scanners. More dubious reasons to own a police scanner include the desire to be alerted to police in the vicinity while driving, or the use of a scanner to assist with planning or executing a crime.
Many countries have laws about how scanners can be used. While law enforcement broadcasts may be public in nature because they are not encrypted, people cannot use them in criminal activity, and decoding transmissions which are encrypted is not legal. Some regions ban the use of devices which can receive only, arguing that legitimate uses would include transmission and reception.