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I was a cryptologic tech in the US Navy (CTRSN, nothing big).  All 'spooks'
in the Navy are required to know the "gist" of "USSID 18", the Navy-way of
naming a particular Presidential "Executive Order".  It outlines what spooks
can and can't do with respect to the privacy of US nationals.

The following information is (of course) UNCLASSIFIED.

The whole issue hangs about what you mean by "wiretap".  If the signal can
be detected by "non-intrusive" means (like radio listening), then it may be
recorded and it may be "analyzed".  "Analyzed" means that it may be either
deciphered and/or radio-location may be used to locate the transmitter.

The catch is this:  Any and all record of the signal and its derivatives
may only be kept for a maximum of 90 days, after which they are destroyed
unless permission is obtained from the US Attorney General to keep them.

Didn't you ever wonder how Coast Guard cutters *find* those drug-runners
in all those tens of thousands of square miles of sea, even in the dark?!?