The terms radio scanner or police scanner generally refer to a communications receiver that is primarily intended for monitoring VHF and UHF landmobile radio systems, as opposed to a receiver used to monitor international shortwave transmissions.

You could say dishonest people, also journalists and everyday people are known to use the radio scanners to snoop in on conversations.

Dialing in to the conversations of emergency services has been occuring for quite a while. The radio scanners used by them to eavesdrop are simply radio receivers capable of track hundreds of frequencies which can not be heard normally using everyday radio devices.

There are many people use radio scanners for fun, however some people use it with evil intentions such as tracking the activities of law enforcement to help in their intentions. Other than being used in law agencies these scanners are used for high frequency communication in corporations and emergency services to keep their transmissions private. Seeing the rising number of break ins taking place in their communication devices the corporations began to broadcast it digitally. This move opened up the market for radio scanners as technology kept pace with the advances created by the corporations. Project 25 is a group of standards for digital radio communications used by safety groups in the United States to help them communicate with each other.

It's similar to European Tetra protocol though not connected to it in any way. The project was introduced after 9/11 .The rules of this protocol state a range of digital frequencies has to be assigned for the use of law enforcement and emergency services. But this move was jeopardized by the advent of digital radio scanners that made the broadcasts readily available to the everyday person as easily as the old scanners worked with high frequency broadcasts.

These mobile radio scanners are available in lots of radio stores that sell electronic devices and of course on the net. Post 9/11 the US government decided to encrypt digital frequencies to stop the public from listening in using mobile radio scanners.

This opened up a lott of debate and heaps of liberal supporters attempted to defend the right of the everyday person to snoop into the transmissions using their right under the information act.These efforts were a waste of time as government chose to encrypt their digital broadcasts. Some of the people tried to buy mobile radio scanners which can decrypt the digital broadcasts but these electronics were legally banned and yanked from the market.

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