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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 more of the radio spectrum and use other modulation types. The traditional use of scanners is to monitor police, fire, Emergency Medical Services, and similar radio systems that use a number of frequencies but with only sporadic use of each.

Contents 1 History and use 2 Legal issues 3 Scanner laws by country 4 See also 5 References 6 External links 6.1 Radio Frequency Sources 6.2 Scanner Manufacturers 6.3 Scanner Laws 6.4 Other links

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.

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 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.^[1]. 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.

A full text copy of the Electronic Communications Privacy Act of 1986 can be found here: "Electronic Communications Privacy Act of 1986"

• United States of America: It is illegal to receive or listen to cellular phone frequencies in the 800 MHz band, or to cordless phone calls, and to use information gained from listening to a scanner in furtherance of the commission of a crime. It is also illegal to use for personal gain information obtained from any radio transmissions not intended for public reception, or to disclose such information to a third party. Several states have laws further restricting the use of scanners. For example, in Minnesota, the mobile use of a scanner in an automobile by anybody other than a police officer, a licensed amateur radio operator, or the holder of a permit from the Minnesota Bureau of Criminal Apprehension is illegal.
• New Zealand: According to the Act 1989 It is legal to possess and use a scanner at any time to tune to any private voice radio (not encrypted data) provided that private information is not passed on or disclosed to any other person(s) or party(s).
• Australia: It is legal to possess a scanner. It is legal to listen to any transmission that is not classified as telecommunication (i.e. anything not connected to the telephone network).
• Mexico: It is legal to have an unlocked scanner and listen to any radio spectrum frequencies including encrypted and cellular band. But according to the Federal Law of General Ways of Communication it is restricted to any individual to spread information obtained on a mass media.
• United Kingdom: The Wireless Telegraphy Act in relation to scanning essentially makes it an offence for any person to 'intercept' any message of which he or she is not the intended recipient.

• Two-way radio
• Trunked radio system
• Communications receiver

There are numerous websites which provide lists of frequencies for emergency services and businesses in various areas of the world. These are among the most prominent.

• Frequency Database for Ireland.
• Police-Scanner.info - The Police Scanner Info-Portal
• RadioReference
• Scanning New Zealand
• United States Federal Communications Commission FCC searchable database of licensed radio frequencies
• Australian Communications and Media Authority ACMA searchable database of licensed frequencies and users
• FlightRadio.com - Aircraft frequencies for your scanner.
• Freq of Nature
• Scanning In Tasmania, Australia
• Monitoring Times Milcom Blog A Radio related blog with military frequencies, callsigns and communications news (including milsat info/frequencies).
• NF2G Scannist Pages A list of frequencies for New York State maintained by Dave Stark, NF2G.
• CARMA (Chicago Area Radio Monitoring Association)

• AOR (Authority on Radio Communications)
• Radio Shack
• Uniden under the Bearcat brand, but also OEM under Radio Shack brand in the United States
• Icom US, CA, AU, NZ
• GRE (formerly exclusively OEM's for Radio Shack in the United States, but as of 2007 also as the "GRE-COM" brand)

• Mobile Scanner & RADAR Detector Laws in the U.S.
• Radio Communications Legislation in Australia - including the use of scanners

• RadioReference.com's Information Wiki
• Information and a database related to radio scanning in Ireland (1400 frequencies)
• A FAQ for scanner users
• A beginner's guide to scanning radios
• A guide to selecting a scanner model
• Incident Broadcast Network - Listen to live scanner feeds from around the USA and the world, for free!
• Radio Scanner Programming Service
• ScannerFeeds.us - Online scanner directory containing 1300+ links.
• Great Falls MT Area live scanner feed and information