This article is from the Motorsport FAQ, by A H Henry bspahh@midge.bath.ac.uk with numerous contributions by others.
20.2.1 USA
In the United States, scanning from your home or at work is perfectly
legal in most situations. The Electronic Communications Privacy Act
of 1986 made it illegal to listen to mobile phones, and a few other
types of communication, but many scanners cover these frequencies,
and it's clear that Americans still listen to whatever they want in
the privacy of their own homes despite the ECPA.
Speaking of privacy, US federal law also requires you to keep what
you hear to yourself and not use the information you hear on your
scanner for personal gain.
Be aware that California, Florida, Indiana, Kentucky, Michigan,
Minnesota, Nebraska, New Jersey, New York, North Dakota, Oklahoma,
South Dakota, Tennessee, and Vermont have laws pertaining to scanning
while in your car. Indiana restricts some portable scanners. You can
find out about these restrictions in a 39 page paperback, ANARC Guide
to U. S. Monitoring Laws, compiled by Frank Terranella, available for
$ 7.50 from ANARC Publications, P.O. Box 462, Northfield, MN 55057.
20.2.2 UK
In the UK, anyone can own a radio scanner, but you may need a licence
to be allowed to use it legally. The air waves are considered to be
government owned. You cannot listen to anything without the
appropriate licence. To receive radio (sound) amateur and broadcasts
the government has decreed that no licence is necessary, although
this has only been the case for the last few years. To receive TV you
must have a licence which is actually used to fund the BBC. To
receive anything else (apart from a few minor exceptions) then in
theory you must have an appropriate licence, and these are not
generally available. For example, a member of the general public
cannot successfully apply for a licence to listen to the police
frequencies.
[ you should not ] make known the contents of any such message,
its origin or destination, its existence, or the fact of its
reception. This also makes lists of scanner frequencies illegal
in the UK.
The authorities do not currently seem very interested in prosecuting
most breaches of this law.
 
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