Reasonable expectations of privacy and novel search technologies: an economic approach.

Author:Penney, Steven

    In both the United States and Canada, the reasonable expectation of privacy test defines the scope of constitutional protection from governmental privacy intrusions. When a court decides that a person has no reasonable expectation of privacy in relation to an investigative technique, there is no "search" or "seizure" within the meaning of the Fourth Amendment of the United States Constitution (1) or [section] 8 of the Canadian Charter of Rights and Freedoms. (2) In such cases, police are free (absent any statutory restriction) to use the technique without first obtaining a warrant or establishing individualized suspicion. (3) When there is a reasonable expectation of privacy, in contrast, police must generally obtain a warrant based on probable cause before conducting the search. (4)

    Unfortunately, the jurisprudence that American and Canadian courts have developed in applying the reasonable expectation of privacy test is notoriously circular, imprecise, and unpredictable. (5) In this Article, I argue that this indeterminacy stems in large measure from the tendency of judges to think of privacy in non-instrumentalist terms. Courts typically view privacy as a fundamental right, rooted in notions of dignity, autonomy, identity, personality, or liberty. (6) And while they often acknowledge the existence of countervailing interests, they generally treat privacy as an unalloyed social good. (7)

    There are several problems with this approach, which I refer to as the "moral" conception of privacy. First, casting privacy as a moral right is normatively questionable. (8) It is not at all clear that privacy is as central to human flourishing as most deontologically-oriented jurists claim.(9) Second, to the extent that it is important, the moral approach does a poor job of identifying the circumstances in which privacy should prevail over countervailing interests, such as the deterrence of crime. Third, neither the Fourth Amendment nor [section] 8 of the Charter protects privacy in a "fundamental" manner; they protect only the right to be free from "unreasonable" searches and seizures. (10) Even gross privacy invasions may be justified when the State can show that they are likely to reveal evidence of serious crimes. (11) As courts in both countries have recognized, constitutional search and seizure decisions (including threshold reasonable expectation of privacy determinations) call for some kind of instrumentalist cost-benefit calculation. (12) Yet by conceptualizing privacy in moral terms, courts have largely failed to perform this calculation with rigor, clarity, or transparency.

    The intent of this Article, then, is to develop a fully instrumentalist approach to the reasonable expectation of privacy test. The obvious place to start is economic analysis. There is a flourishing literature on the law and economics of privacy. Drawing mostly from the economics of information, (13) legal economists have taken on a wide variety of privacy issues. (14) There have been few attempts, however, to apply economic insights to search and seizure law. (15) This Article aims to help fill this gap. I provide an accounting of the costs and benefits of governmental privacy intrusions and propose a framework for making reasonable expectation of privacy decisions that maximize social welfare.

    In contrast to the prevailing moral approach, which treats privacy as a fundamental right, the economic approach views it as a normatively neutral aspect of self-interest: the desire to conceal and control potentially damaging personal information. In this view, privacy should not be protected when its primary effect is to impede the optimal deterrence of crime. However, in other cases legal protections against governmental surveillance may enhance social welfare by encouraging productive transactions, diminishing the costs of non-legal privacy barriers, and limiting suboptimal policing practices such as discriminatory profiling and the enforcement of inefficient criminal prohibitions. Economics and public choice theory can also help to minimize decision-making error by predicting which legal actors--police, legislatures, or courts--are best placed to make optimal trade-offs between privacy and crime control.

    The Article proceeds as follows. In Section II, I briefly describe the American and Canadian Supreme Courts' reasonable expectation of privacy doctrines and highlight their chief inadequacy: the indeterminacy of the "public exposure" and "intimacy" doctrines that the Courts have used to decide whether to regulate novel search technologies. Section III outlines the economic approach to the reasonable expectation of privacy test. Sections IV and V apply this approach to two novel search technologies: infrared imaging and location tracking. This analysis suggests that courts should recognize a reasonable expectation of privacy in the latter case, but not the former. Section VI concludes.


    The use of the reasonable expectation of privacy test dates from the United States Supreme Court's 1967 decision in Katz v. United States. (16) Katz famously departed from the prevailing conception of Fourth Amendment searches as physical trespasses into "constitutionally-protected" areas. (17) In deciding that the placement of an electronic listening and recording device outside a public telephone booth was a search, Justice Stewart declared for the majority that the Fourth Amendment protected "people, not places," (18) and the surreptitious interception of the petitioner's conversation "violated the privacy upon which he justifiably relied." (19) The "reasonable expectation" phraseology, however, stems from Justice Harlan's concurring opinion. Harlan stated, in language later adopted by a majority of the Court, that to be considered a search, it must be shown both that a person "exhibited an actual (subjective) expectation of privacy and ... that the expectation be one that society is prepared to recognize as 'reasonable.'" (20) In its first decision interpreting [section] 8 of the Charter, the Supreme Court of Canada adopted the same approach. (21)

    How, then, have courts gone about deciding what constitutes a "reasonable expectation of privacy"? This is not the place to summarize the reams of doctrine on the question. (22) It will be helpful, however, to provide some sense of how the American and Canadian Supreme Courts have applied the test to novel search technologies.

    Not surprisingly (and contrary to Justice Harlan's dictum in Katz), courts have not considered the existence of a subjective expectation of privacy to be a necessary condition of constitutional protection; (23) otherwise, police could simply advertise their intention to monitor everything capable of being monitored. (24) Moreover, people who were more suspicious or aware of governmental surveillance would receive less constitutional protection than those more trusting or ignorant. (25) The focus has instead been on the second component of Harlan's formula: whether an expectation of privacy is "reasonable."

    Like other reasonableness standards, on its face, the reasonable expectation of privacy test is extremely vague. Insofar as it gauges "expectations" of privacy (both subjective and objective) in relation to prevailing social and technological conditions, it is also tautological. As Wasserstrom and Seidman have put it, "Reasonable expectations are defined by reference to a current reality that includes the very practices under attack, rather than by reference to the kinds of expectations people would have in a normatively attractive society." (26) The test's language implies that we can expect less and less constitutional protection for privacy as technology continues to enhance the power and lower the costs of surveillance. (27)

    To be sure, courts have attempted to suffuse the test with normative content. (28) They have pointed out many virtues of privacy and catalogued myriad factors influencing reasonable expectation of privacy decisions. But the key conceptual tools that the courts have developed to aid these decisions--the public exposure and intimacy doctrines--have produced little jurisprudential consistency, predictability, or consensus.


      The public exposure doctrine exempts from constitutional protection information voluntarily disclosed to the public. As Justice Stewart explained in Katz, "What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected." (29) The doctrine is a natural outgrowth of liberal moral theory. If rational, autonomous agents freely choose to expose information to the public, then they cannot complain if others use that information against them.

      It seems axiomatic that information voluntarily released into the public domain cannot attract a reasonable expectation of privacy. The problem, of course, is that the meanings of "voluntary" and "public" are sometimes contestable. People frequently divulge information, for example, assuming that it will be used only for certain limited purposes. (30) They may also subject themselves to observation assuming that their identities will likely remain anonymous. But what happens when technological search tools upend these assumptions? Can we still say that there has been a voluntary exposure?

      Judges have given divergent answers to these questions. For example, the American and Canadian Supreme Courts have differed on the question of whether the electronic interception of speech constitutes a "search" when one of the speakers is an undercover police informant. As discussed, the United States Supreme Court established in Katz that surreptitious interceptions of private communications are Fourth Amendment searches. Soon after...

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