Originalism and the Fourth Amendment:
In response to Jim's post below, surprisingly little of relevance is known about the original purpose of the Fourth Amendment. There was no policing at the time of the Framing, at least as we conceive of it today, and the Framers were mostly thinking about limiting particular types of very broad warrants that the King had permitted to search physical places and things. In any event, the Supreme Court wrestled with the issues that Jim raises below in three major cases: Olmstead v. United States (1928), Berger v. New York (1967), and Katz v. United States (1967). The gist of the cases (to really really oversimplify matters) is that Jim's argument had five votes in Olmstead, but became a minority view by the time of Berger and Katz.

  Indeed, Jim's argument sounds a lot like Justice Black's solo dissent from Berger. An excerpt:
    Eavesdroppers have always been deemed competent witnesses in English and American courts. The main test of admissibility has been relevance and first-hand knowledge, not by whom or by what method proffered evidence was obtained. It is true that, in England, people who obtained evidence by unlawful means were held liable in damages, as in Entick v. Carrington, 19 How.St.Tr. 1029. But even that famous civil liberties case made no departure from the traditional common law rule that relevant evidence is admissible even though obtained contrary to ethics, morals, or law. And, for reasons that follow, this evidentiary rule is well adapted to our Government, set up as it was to "insure domestic tranquility" under a system of laws. * * *
  While the electronic eavesdropping here bears some analogy to the problems with which the Fourth Amendment is concerned, I am by no means satisfied that the Amendment controls the constitutionality of such eaves-dropping. As pointed out, the Amendment only bans searches and seizures of "persons, houses, papers, and effects." This literal language imports tangible things, and it would require an expansion of the language used by the framers, in the interest of "privacy" or some equally vague judge-made goal, to hold that it applies to the spoken word. It simply requires an imaginative transformation of the English language to say that conversations can be searched and words seized.
  Interestingly, none of the current Justices seem to be interested in returning to Justice Black's approach. Occasional originalist Justice Scalia has written opinions that suggest an interest in creating new rules that capture the original role of the Fourth Amendment in light of technological change — see, for example, his opinion in Kyllo v. United States — but I don't think there are any votes on the current Court for Justice Black's approach.