Cite as: 533 U. S. 27 (2001)
Opinion of the Court
home activities are "intimate" and which are not. And even when (if ever) that jurisprudence were fully developed, no police officer would be able to know in advance whether his through-the-wall surveillance picks up "intimate" details— and thus would be unable to know in advance whether it is constitutional.
The dissent's proposed standard—whether the technology offers the "functional equivalent of actual presence in the area being searched," post, at 47—would seem quite similar to our own at first blush. The dissent concludes that Katz was such a case, but then inexplicably asserts that if the same listening device only revealed the volume of the conversation, the surveillance would be permissible, post, at 49-50. Yet if, without technology, the police could not discern volume without being actually present in the phone booth, Justice Stevens should conclude a search has occurred. Cf. Karo, 468 U. S., at 735 (Stevens, J., concurring in part and dissenting in part) ("I find little comfort in the Court's notion that no invasion of privacy occurs until a listener obtains some significant information by use of the device. . . . A bathtub is a less private area when the plumber is present even if his back is turned"). The same should hold for the interior heat of the home if only a person present in the home could discern the heat. Thus the driving force of the dissent, despite its recitation of the above standard, appears to be a distinction among different types of information—whether the "homeowner would even care if anybody noticed," post, at 50. The dissent offers no practical guidance for the application of this standard, and for reasons already discussed, we believe there can be none. The people in their houses, as well as the police, deserve more precision.6
6 The dissent argues that we have injected potential uncertainty into the constitutional analysis by noting that whether or not the technology is in general public use may be a factor. See post, at 47. That quarrel,
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