United States Code TITLE 18 - CRIMES AND CRIMINAL PROCEDURE
PART I - CRIMES
CHAPTER 119 - WIRE AND ELECTRONIC COMMUNICATIONS
INTERCEPTION AND INTERCEPTION OF ORAL COMMUNICATIONS

(16) ''readily accessible to the general public'' means, with
respect to a radio communication, that such communication is not
-
(A) scrambled or encrypted;
(B) transmitted using modulation techniques whose essential
parameters have been withheld from the public with the
intention of preserving the privacy of such communication;
(C) carried on a subcarrier or other signal subsidiary to a
radio transmission;
(D) transmitted over a communication system provided by a
common carrier, unless the communication is a tone only paging
system communication; or
(E) transmitted on frequencies allocated under part 25,
subpart D, E, or F of part 74, or part 94 of the Rules of the
Federal Communications Commission, unless, in the case of a
communication transmitted on a frequency allocated under part
74 that is not exclusively allocated to broadcast auxiliary
services, the communication is a two-way voice communication
by radio;
[CITE: 18 U.S.C 2510]http://www4.law.cornell.edu/uscode/18/2510.html