The history of the police scanner goes clear back to the early 1930’s. The police would broadcast through a local AM radio Station. Anyone with a radio could hear the calls. A conventional radio system is basically full of frequencies. Frequencies are the channels of communication.
To hear transmissions you must program certain channels into the scanner. The first type of police scanners were crystal controlled with about four channels. To listen you would have to have a quartz-crystal tuned to that frequency and plugged into an internal slot. Each of those crystals would cost around $7.00 and eventually become very expensive to upkeep.
Then in the late 1970’s scanners that were programmable were invented. It had a keypad that you would enter frequencies with and the memory of the scanner would save all your frequencies. Then the trunked radio system came out and it allowed you to keep track of five to thirty channels or frequencies. A site controller is where users were automatically assigned frequencies. Like the emergency departments would have one frequencies or truckers would have another frequency. These types are harder to monitor because you are often switching channels even in between conversations.
Today, you have digital trunking scanners. It is a computer that encodes a voice transmission into streams of data and then the receiver will decode it so that an audible voice can be heard. They were first introduced in 2002 by Uniden and then in 2003, Radio Shack released their digital scanner. These are great to use because you can say things over the radio and it not be heard, but only by those who can decode it, which would be a few people. The only people who could decode the codes is those who are programmed for the channel.
Police scanners are nice to have because they are something different from TV and radio. You can sit in your backyard and understand why the police are going up the road and you know that it would be something to become alarmed over or something not to frit over. Police scanners are purchased because a person belongs to one of the emergency departments or just for the interest in the community.
Many times, there are announcements on a police scanner that will first be aired before any TV stations get a hold of the information. For example, you will be notified first from a police scanner about any tornados that touchdown or if the weather gets too sever before the news airs the information. This type of information is announced from the National Weather Service and is completely trust worthy. Police scanners can also be entertaining as much as informational because of all the silly things people will say over the air.