Because of argument creep, it's important to be careful about relying on analogies when examining a technological change. Instead of simply applying old standards relevant to old technologies to new situations, the courts must reevaluate each technology, not only in terms of what it does at a basic level, but also -- and more important -- in terms of how society feels about it.
Now, that can seem like a pretty squishy standard for judicial decision-making, but the question of how society feels is explicitly embedded in the Fourth Amendment in the word "unreasonable." This word, at least in part, asks for society's judgment about a government's action; it asks how society feels.
The D.C. Circuit Court of Appeals understood this and intuited, in the Jones case, that society does not feel the same way about GPS as it did about beepers (to say nothing of binoculars). When that lower court reviewed Jones's case, it ruled (pdf):
Society recognizes Jones's expectation of privacy in his movements over the course of a month as reasonable, and the use of the GPS device to monitor those movements defeated that reasonable expectation. As we have discussed, prolonged GPS monitoring reveals an intimate picture of the subject's life that he expects no one to have -- short perhaps of his spouse.
In other words, it took into account the subjective societal standard of "reasonable" and determined that GPS monitoring did not live up to Constitutional snuff.
The challenge is that this sort of judgment -- the ability to see, somehow, the societal attitude about a particular surveillance technique -- does not come easy to the courts, in part because it does not come easy to society as a whole. Technological changes can quicken society's pulse, inspiring both fearful denunciations (it will ruin the children!) and utopian visions. The implications of new technologies are usually not clear from the outset, and it can take a while for the dust to settle before a Court can reasonably step in to make an assessment.
Perhaps the most vivid example of this confusion is the question of what (or who) will count as a legal person -- and therefore entitled to due process and equal protection rights under the 14th amendment -- in the future, an issue explored in a provocative essay by James Boyle. Boyle writes:
My point is a simple one. In the coming century, it is overwhelmingly likely that constitutional law will have to classify artificially created entities that have some but not all of the attributes we associate with human beings. They may look like human beings, but have a genome that is very different. ... They may be physically dissimilar to all biological life forms -- computer-based intelligences, for example -- yet able to engage in sustained unstructured communication in a way that mimics human interaction so precisely as to make differentiation impossible without physical examination.
The answer may seem obvious -- how could you confuse a robot for a human? But then pause to consider that when the Constitution was written, slaves did not have the full rights of citizens. Neither did women. We continue to hotly debate whether a fetus is a person. The definition of a person is not exactly stable. In the coming years, we may find ourselves re-evaluating this fundamental idea, one that underlies our entire legal system, in light of technological advances from the fields of robotics and synthetic biology.