Police Radio Scanners

The air around you is bursting with radio waves. You know that you can turn on your AM/FM radio in your car and receive dozens of stations. You can flip on a CB radio and receive 40 more (120 includes single side band units). You can flip on a TV and receive a lot of broadcast channels. Cell phones send and receive hundreds of frequencies. And this is really just the tip of the radio spectrum iceberg. There are tens of thousands of other radio broadcasts and conversations are zooming past you as you read this - police officers, firefighters, ambulance drivers, paramedics, sanitation workers, space shuttle astronauts, race car drivers and even railroad conductors are transmitting radio waves all around you at this very moment!

To tap into this ocean of electromagnetic dialogue and hear what all of these people are talking about, all you need is a scanner. A scanner is basically a radio receiver capable of receiving multiple signals. Generally, scanners pick up signals in the VHF to UHF range

What is a Radio Scanner?

A scanner is a radio receiver that can automatically tune, or scan, two or more discrete frequencies, stopping when it finds a signal on one of them and then continuing scanning when that frequency goes silent. Generally, scanners cover the non-broadcast radio bands between 30 and 950 MHz using FM, although there are models that cover much more of the radio spectrum and use other modulation types. The traditional use of scanners is to monitor police, fire, Emergency Medical Services (EMS) and similar radio systems that use a number of frequencies but with only sporadic use of each.

Radio Scanner History

Scanners developed from earlier tunable and fixed-frequency radios that received one frequency at a time. Non-broadcast radio systems, such as those used by public safety agencies, do not transmit continuously. With a radio fixed on a single frequency, many minutes could pass between signals, while other frequencies used in the area might be active. The scanning function allows the radio to progress through a routine of pre-programmed channels, or between two limits which define a band of frequencies. It will dwell on an active frequency and will usually resume scanning its defined routine until activity is again found.

Popular amongst hobbyists, railfans, off duty emergency services personnel, reporters, corporate spies, criminals and lawyers, scanners allow chosen frequencies to be stored in memory banks to allow them to be monitored later and will only stop scanning when there is a signal strong enough to break the radio's squelch setting.

Scanners first became popular and widely available during CB Radio's heyday in the 1970s. The first scanners often had between four and ten channels and required a separate crystal for each frequency received. Modern programmable scanners allow hundreds or thousands of frequencies to be entered via a keypad and stored in various 'memory banks' and can scan at a rapid rate due to modern microprocessors.


A hand-held wide band communications receiver. Many recent models will allow scanning of the specific DCS or CTCSS code used on a specific frequency should it have multiple users. One memory bank can be assigned to air traffic control, another can be for local marine communications, and yet another for local police frequencies. These can be switched on and off depending on the user's preference. Most scanners have a weather radio band, allowing the listener to tune into weather radio broadcasts from a NOAA transmitter.

Some scanners are equipped with Fire-Tone out. Fire tone out decodes Quik call II tones and acts as a pager when the correct sequence of tones is detected.

Active frequencies can be found by searching the internet and frequency reference books or can be discovered through a radio's search function. An external antenna for a desktop scanner or an extendable antenna for a hand held unit is a good idea for optimum performance.

Radio Scanner Legal Use Issues

Radio scanners have had a mixed response from law enforcement agencies and sometimes championed by those supporting civil liberties. In some communities, law enforcement has chosen to encrypt their communications. Although scanners capable of following trunked radio systems and demodulating some digital radio systems such as APCO Project 25 are available, decryption-capable scanners would be a violation of United States law and possibly laws of other countries.

A law passed by the Congress of the United States (under the pressure from cellular telephone interests) prevented scanners sold in the U.S. from tuning the 800 MHz cellular band. Later, the law was amended to make it illegal to modify radios to receive those frequencies, and also to sell radios that could be easily modified to do so. This law remains in effect even though few cellular subscribers still use analog technology. Typically, there are Canadian and European "unblocked" versions available, however these are illegal to import into the U.S. The cordless phone bands at 43.720--44.480, 46.610--46.930 MHz and 902.000 – 906.000 MHz can still be picked up by many scanners. These bands, too, are illegal to monitor in the U.S. The proliferation of scanners led to cordless phone manufacturers going to a much more secure 2.4 GHz system using spread-spectrum technology. Certain states in the U.S., such as New York and Florida, prohibit the use of scanners in a vehicle unless licensed by the FCC.

In the United Kingdom and France, it is illegal to listen to almost anything outside the amateur radio and broadcast bands. Canada allows any analog transmission to be monitored but content of the communication may not be disclosed. In some parts of the United States, there are extra penalties for the possession of a scanner during a crime, and some states, such as Michigan, also prohibit the possession of a scanner in any place by a convicted felon. Other countries consider possession of a scanner at any time an offense.

In the United States, the general guidelines to follow when using a radio scanner are that it is illegal to:

• listen in on cellular and cordless phone calls
• intercept encrypted or scrambled communications
• sell or import radio scanners that are capable of receiving cellular phone frequencies (Note: This rule does not apply to sales by individuals and radio scanners made before 1985)
• modify radio scanners so that cellular phone frequencies can be received
• use information received for personal gain (A common example is where a taxi driver listens to a competitor's dispatch channel to steal a customer)
• use information received to aid in the commission of a crime, or
  disclose information received to other persons