[Prop 8 stuff separated.]
Orin Kerr, an expert in the field, flags an interesting case that I first saw referenced on the news update portion of the paper he singles out as likely to support it (NYT; I found that a bit catty). Also discussed in this informative Washington Post article, it concerns a libertarian leaning panel striking down GPS monitoring without a warrant. Kerr doesn't buy it, including its "mosaic theory" that a search can be problematic as a whole. (One comment compared it to torture being a result of the sum of the interrogation's parts, which seems appropriate). To wit:
“A single trip to a gynecologist’s office tells little about a woman, but that trip followed a few weeks later by a visit to a baby supply store tells a different story,” Ginsburg wrote.
He added, “A person who knows all of another’s travels can deduce whether he is a weekly churchgoer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups — and not just one such fact about a person, but all such facts.”
Kerr also thinks Supreme Court precedent that allows attaching beepers to cars [late update: actually, it isn't even that -- it involved putting a beeper in a container of ether which a person then obtained without knowing it; the issue of placing a beeper on the car or item in a person's immediate possession wasn't even at issue ... more evidence that Kerr is simply misguided to think the precedents, involving much simpler technology and notably different facts are so clearly on point] are applicable here. In somewhat vague language, the Supreme Court -- in a portion latched on by the panel -- implied not all beeper-like searches of a certain scope would be allowed. I think GPS technology is quite different from beepers, so comparing the two seems to me a bit "unreasonable," but wouldn't be surprised if the Supreme Court agrees with him. The discussion also addresses the logic of the opinion, which is somewhat an inside baseball matter.
Two conclusions: given the change of technology and a circuit split, see the article, Supreme Court/21st Century (the beeper cases from the early 1980s) review is warranted. If not now, soon enough. Also, given modern information collection, the "mosaic theory" or some offshoot would be a principled way to apply the Fourth Amendment. It's a different question if that is the path that will be taken.