The positive law model has . . . flaws as a universal guide. Like the probabilistic model, the positive law model provides an accurate proxy for the reasonableness of police practices in many cases. Positive law that restricts access to information and places often reflects widely shared notions of which accesses cause significant harms and which do not. Courts, legislatures, and agencies will tend to promulgate rules restricting access to a person’s private material when unfettered access will be harmful, which is a major factor in determining whether a particular government practice is reasonable per se or reasonable only in context. This means that government practices that violate positive law will often be reasonable only in context, and those practices that do not will often be reasonable per se.
Physical intrusions into the home provide an obvious example. Breaking into to your house interferes with your property rights; it also reflects a deeply invasive affront to your privacy and security. On the other hand, watching your house from a public street does not violate positive law; while it may be a bit creepy, it does not amount to a severe invasion of your privacy. In this context, positive law nicely matches our intuitions as to which kinds of police practices should be permitted without a warrant. The positive law model provides a useful proxy to determine when a government invasion violates a reasonable expectation of privacy.
But much like the probabilistic model, the positive law model does not work in every case. In many circumstances, positive law will not accurately capture whether police practices are per se reasonable. This is true for two primary reasons. First, positive laws are enacted for a wide range of reasons that may have nothing to do with whether access by criminal investigators would be reasonable per se. Consider the FAA regulations analyzed in Florida v. Riley, the helicopter flyover case. The FAA presumably drafted those regulations to minimize noise and deter accidents, not to limit the police. Whether the police happened to fly over or under FAA airspace limits has no significant connection to whether particular police flyovers are reasonable only if justified by a warrant. Similarly, imagine a person lives on a 100-acre farm with their small house in the center. Trespassing a few feet onto that person’s property will violate his property rights but not infringe on his privacy. In that setting, positive law does not accurately track the reasonableness of the government’s investigation.
The positive law model may also be insufficient when technology or social practice changes rapidly. The story is a familiar one, as it tracks the standard explanation for the move from Olmstead to Katz. Technology tends to shift the privacy implications of different law enforcement steps. New technologies can divorce privacy and social norms from property law and other statutory and regulatory protections. New technological surveillance tools make it possible to invade privacy without interfering with property or other laws, and they can also make it possible to establish privacy without harnessing positive law. As a result, technological change can make the function of positive law largely arbitrary; it no longer serves the same function it might if the technology remained stable. A test that focuses entirely on positive law such as property will be underprotective with technological surveillance techniques and may prove overprotective with other techniques.
Like the probabilistic model, positive law accurately distinguishes per se and contextually reasonable practices in some cases but not others. As a result, it cannot provide an exclusive guide to what makes an expectation of privacy reasonable.