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88 Texas Law Review 1475 (2010)


This Article explains why the government’s physical surveillance can reach a point in terms of duration and intensity that it becomes a “search” under the Fourth Amendment. As references, Katz v. United States and Kyllo v. United States stand out from the canon. Katz, decided in 1967, swept away a prior emphasis on property rights and trespass laws to hold that the electronic monitoring of a phone booth was a search. Since then, the two-part test from Justice Harlan’s concurring opinion has received as much attention as the totality-of-the-circumstances test in Justice Stewart’s majority opinion. Kyllo, decided just months before 9/11, ruled that the government’s use of a thermal-imaging device from outside a house was a search. For the era after 9/11, a blend of Justice Harlan’s test in Katz with Justice Scalia’s opinion in Kyllo reproduces Justice Stewart’s test, a more open-ended test which makes room for property, liberty, secrecy, anonymity, autonomy, and privacy, as well as other values that may undergird the “right of the people to be secure in their persons, houses, papers, and effects.” For the new age of terror, Justice Stewart’s test helps not only on one issue of physical surveillance but also opens up new approaches to data mining, the use of GPS devices, and other issues at the intersection of national security, privacy, and technology.