The history of the police scanner clearly dates back to the early 1930s. The police would broadcast over a local AM radio station. Anyone with a radio could listen to the calls. A conventional radio system is basically full of frequencies. Frequencies are the channels of communication.
To listen to broadcasts, 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 connected to an internal slot. Each of those crystals would cost around $7.00 and would eventually become very expensive to maintain.
Then, in the late 1970s, programmable scanners were invented. It had a keyboard that you entered frequencies with and the scanner’s memory stored all your frequencies. Then the trunked radio system came along and allowed you to track from five to thirty channels or frequencies. A site controller is where users are automatically assigned frequencies. Like emergency departments would have one frequency or truck drivers would have another frequency. These guys are harder to monitor because they often change channels even between conversations.
Today, you have digital trunking scanners. It is a computer that encodes a voice transmission into data streams and is then decoded by the receiver 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 not be heard, but only by those who can decode them, which would be a few people. The only people who can decode the codes are those who are programmed for the channel.
It is good to have police scanners because they are something different from television and radio. You can sit in your backyard and understand why the police are coming up the driveway and you know that would be something to be alarmed about or something not to be scared about. Police scanners are purchased because a person belongs to one of the emergency departments or simply out of interest in the community.
Many times, there are advertisements on a police scanner that will be broadcast first before television stations get the information. For example, a police scanner will first notify you of any tornadoes that touch down or if the weather becomes too severe before the news broadcasts the information. This type of information is announced by the National Weather Service and is completely reliable. Police scanners can also be both entertaining and informative because of all the silly things people will say on air.