Although no single rubric definitively resolves which expectations of privacy are entitled to protection, the analysis is informed by historical understandings “of what was deemed an unreasonable search and seizure when [the Fourth Amendment] was adopted.” Carroll v. United States, 267 U.S. 132, 149 (1925). On this score, our cases have recognized some basic guideposts. First, that the Amendment seeks to secure “the privacies of life” against “arbitrary power.” Boyd v. United States, 116 U.S. 616, 630 (1886). Second, and relatedly, that a central aim of the Framers was “to place obstacles in the way of a too permeating police surveillance.” United States v. Di Re, 332 U.S. 581, 595 (1948).
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