This morning, the Supreme Court handed down its decision in United States v. Jones, the GPS tracking case, deciding unanimously that the government violated the defendant’s Fourth Amendment rights when it installed a wireless GPS tracking device on the undercarriage of his car and used it to monitor his movement’s around town for four weeks without a search warrant.

Despite the unanimous result, the court was not unified in its reasoning. Five Justices signed the majority opinion, authored by Justice Scalia, finding that the Fourth Amendment “at bottom . . . assure[s] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted” and thus analyzing the case under “common-law trespassory” principles.

Justice Alito wrote a concurring opinion, signed by Justices Ginsburg, Breyer, and Kagan, faulting the majority for “decid[ing] the case based on 18th-century tort law” and arguing instead that the case should be decided under Katz’s “reasonable expectations of privacy” test. Applying Katz, the four concurring Justices would have found that the government violated the Fourth Amendment because “long-term tracking” implicated a reasonable expectation of privacy and thus required a warrant.

Justice Sotomayor, who signed the majority opinion, wrote a separate concurring opinion, but more on that in a second.

I think the Jones court reached the correct result in this case, and I think that the three opinions in this case represent a near-optimal result for those who want the Court to recognize how its present Fourth Amendment jurisprudence does far too little to protect privacy and limit unwarranted government power in light of recent advances in surveillance technology. This might seem counter-intuitive. I predict that many news stories about Jones will pitch it as an epic battle between Scalia’s property-centric and Alito’s privacy-centric approaches to the Fourth Amendment and quote people expressing regret that Justice Alito didn’t instead win the day. I think this would focus on the wrong thing, underplaying how today’s three opinions–all of them–represent a significant advance for Constitutional privacy, for several reasons:

1. Justice Alito? Maybe I’m not a savvy court watcher, but I did not see this coming. The fact that Justice Alito wrote such a strong privacy-centric opinion suggests that future Fourth Amendment litigants will see a well-defined path to five votes, especially since it seems like Justice Sotomayor will likely provide the fifth vote in the right future case.

2. Justice Scalia and Thomas showed restraint. The majority opinion goes out of its way to highlight that its focus on property is not meant to foreclose privacy-based analyses in the future. It uses the words “at bottom” and “at a minimum” to hammer home the idea that it is supplementing Katz not replacing it. Maybe Justice Scalia did this to win Justice Sotomayor’s vote, but even if so, I am heartened that neither Justice Scalia nor Justice Thomas thought it necessary to write a separate concurrence arguing that Katz’s privacy focus should be replaced with a focus only on property rights.

3. Justice Sotomayor does not like the third-party doctrine. It’s probably best here just to quote from the opinion:

More fundamentally, it may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties. E.g., Smith, 442 U.S., at 742; United States v. Miller, 425 U.S. 435, 443 (1976). This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks. People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers. Perhaps, as JUSTICE ALITO notes, some people may find the “tradeoff” of privacy for convenience “worthwhile,” or come to accept this “dimunition of privacy” as “inevitable,” post, at 10, and perhaps not. I for one doubt that people would accept without complaint the warrantless disclosure to the Government of a list of every Web site they had visited in the last week, or month, or year. But whatever the societal expectations, they can attain constitutionally protected status only if our Fourth Amendment jurisprudence ceases to treat secrecy as a prerequisite for privacy. I would not assume that all information voluntarily disclosed to some member of the public for a limited purpose is, for that reason alone, disentitled to Fourth Amendment protection.

Wow. And Amen. Set your stopwatches: the death watch for the third-party doctrine has finally begun.

4. This was the wrong case for a privacy overhaul of the Fourth Amendment. Most importantly, I’ve had misgivings about using Jones as the vehicle for fixing what is broken with the Fourth Amendment. GPS vehicle tracking comes laden with lots of baggage–practical, jurisprudential and atmospheric–that other actively litigated areas of modern surveillance do not. GPS vehicle tracking happens on public streets, meaning it runs into dozens of Supreme Court pronouncements about assumption of risk and voluntarily disclosure. It faces two prior precedents, Karo and Knotts, that need to be distinguished or possibly overturned. It does not suffer (as far as we know) from a long history of use against innocent people, but instead seems mostly used to track fugitives and drug dealers.

For all of these reasons, even the most privacy-minded Justice is likely to recognize caveats and exceptions in crafting a new rule for GPS tracking. Imagine if Justice Sotomayor had signed Justice Alito’s opinion instead of Justice Scalia’s. We would’ve been left with a holding that allowed short-term monitoring but not long-term monitoring, without a precise delineation between the two. We would’ve been left with the possible new caveat that the rules change when the police investigate “extraordinary offenses,” also undefined. These unsatisfying, vague new rules would have had downstream negative effects on lower court opinions analyzing URL or search query monitoring, or cell phone tower monitoring, or packet sniffing.

Better that we have the big “reinventing Katz” debate in a case that isn’t so saddled with the confusions of following cars on public streets. I hope the Supreme Court next faces a surveillance technique born purely on the Internet, one in which “classic trespassory search is not involved.” If the votes hold from Jones, we might end up with what many legal scholars have urged: a retrenchment or reversal of the third-party doctrine; a Fourth Amendment jurisprudence better tailored to the rise of the Internet; and a better Constitutional balance in this country between privacy and security.