The Fourth Amendment to the US Constitution seems straightforward on its face: At its core, it tells us that our “persons, houses, papers, and effects” are to be protected against “unreasonable searches and seizures.” Before any government agent can perform a search or seizure, they must first obtain a warrant, based on “probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”
For courts, however, arriving at satisfactory interpretations of these principles has been anything but straightforward. During a recent conversation on Twitter with Orin Kerr, Jacob Appelbaum, and Jennifer Granick, we discussed the fact that interpretations that involve physical spaces and objects can generally be understood by the average citizen, as our intuitions make good guides when deciding what is and is not private in the physical, tangible world. This mutual understanding between citizen and government helps us preserve the protections articulated within the Fourth Amendment through our ability to spot government overreach and abuse.
Our intuitions about privacy run into difficulties, however, when our use of technology forces us to use metaphors to describe new situations and possibilities. We grew comfortable with, for example, talking about the Internet as a sort of “place” we would go, which was easier, perhaps, than trying to describe packets of data being routed between servers. Before too long, courts were making arguments about computer “trespass,” as if we were actually setting foot on someone’s computer. These inexact metaphors can have serious consequences in the real (physical) world, which is especially true for our current thinking about the Fourth Amendment.
In the 1967 case of Katz v. United States, the Supreme Court called this mutual understanding a “reasonable expectation of privacy,” and made it the standard for deciding when Fourth Amendment protections apply — a standard we continue to follow today. This standard depends on our understanding of what we expect to be private and what we do not. In Katz, for instance, the defendant made a telephone call not from his home, but from a public phone booth, which could be seen by anyone on the street, including the police. The fact that Katz closed the door to the phone booth indicated to the Court that he expected his conversation to be private, just as if he were using the telephone in his own home. This logic depends on an accepted understanding of walls and doors as physical and symbolic means of keeping eavesdroppers away from our private conversations. But what happens when technology takes us out of the realm of physical walls and doors, causing us to lose at least some ability to understand the boundaries the Fourth Amendment sets on government searches and seizures?
For example, it is well-established — and generally understood — that the contents of any sealed letters or packages we send through the Postal Service are considered private, and they “can only be opened and examined under [a] warrant, issued upon  oath or affirmation, particularly describing the thing to be seized, as is required when papers are subjected to search in one’s own household.” The only exceptions to this rule are the observations of the letter’s properties one can observe without opening it, such as its size, its weight, and the address information written on it. Can the same be said about our email? One can’t touch or otherwise physically manipulate an email message like one written on paper, but we still tend to think of email messages as a contemporary analogue to “letters.” Does it therefore follow that we have the same expectation of privacy in our email messages as we do our letters and packages?
Read the full post at Just Security.