It’s been quite a week, what with the Guardian newspaper’s Glenn Greenwald publishing a leaked NSA surveillance order to Verizon, and then last night’s revelations about how the military has directly tapped in to the servers of major internet companies like Google, Apple, Microsoft and Facebook. What began as a major controversy about phone and internet records has exploded into the biggest surveillance story of a decade, littered with scores of privacy-bombshells.

Particularly in light of these disclosures, the Massachusetts Supreme Judicial Court Commonwealth v. Rousseau decision, released this week, deserves wide discussion.

Quite simply, Rousseau cuts to the heart of the question raised by the NSA surveillance scandal: does the government need to have any individualized suspicion to extensively spy on us, or have we done away with that most basic tenet of our constitutional protections against unreasonable government searches?

Thankfully, the court answered the right way.

In short, the state’s highest court ruled that the government must have probable cause and provide judicial oversight before tracking us for extended periods of time using GPS devices. If it were up to the Massachusetts SJC, the NSA would be barred from doing lots of what we have just confirmed it has been doing for years.

Rousseau stems from the 2007 convictions of two Massachusetts men, John Rousseau and Michael Dreslinski, on counts of arson and other crimes. State police officers had used information gleaned from a GPS tracking device placed on Dreslinski’s car as evidence that helped convict both men.

Both men appealed the convictions, arguing, the court writes, “that the warrant which authorized the State police to attach the GPS device to Dreslinski’s car for 31 days was not supported by probable cause and therefore violated the Fourth Amendment to the United States Constitution and art. 14 of the Massachusetts Declaration of Rights.”

In response, the government argued Rousseau had no right to challenge the constitutionality of the GPS tracking that helped convict him, because he was neither the driver nor the owner of the car the police were tracking.

That doesn’t make sense. Thankfully, the SJC doesn’t think so, either:

Rousseau, as a passenger in the vehicle, also has standing because he had a reasonable expectation that his movements would not be subjected to extended electronic surveillance by the government through use of GPS monitoring.

That’s great news. But it gets even better. .

Furthermore, the court ruled, “under art. 14, a person may reasonably expect not to be subjected to extended GPS electronic surveillance by the government, targeted at his movements, without judicial oversight and a showing of probable cause.” (Article 14 is essentially the Massachusetts version of the Fourth Amendment; you can read it here.)

Remember three key phrases from that sentence: “extended GPS surveillance,” “judicial oversight,” and “probable cause.” The court ruled that, under the Massachusetts Declaration of Rights, if the government wants to watch our movements for an extended period of time (which at the very least is 31 days), then it needs to go to a Judge and prove that it is has probable cause to do so. 

As ACLU of Massachusetts’ Legal Director, Matthew Segal, who co-wrote an amicus brief in Rousseau, says:

Today's ruling by the Supreme Judicial Court is a huge victory for anyone who does not want the government to track their movements. Relying on the Massachusetts Declaration of Rights, the court held that the police generally cannot track someone using GPS surveillance unless they secure "judicial oversight" and make "a showing of probable cause." Although the case itself concerned a passenger in a truck he did not own, the SJC's ruling was not at all limited to that circumstance. Instead, the SJC made clear that its ruling applies to essentially everyone in Massachusetts.

Not only does the ruling apply to everyone in Massachusetts. The requirement to obtain “judicial oversight” and a “showing of probable cause” before the government can use GPS surveillance to track us for an extended period of time arguably extends well beyond the placement of a GPS tracking device onto a vehicle.

As an ACLU study showed, law enforcement nationwide regularly subpoena detailed information about our travel patterns from our cell phone companies. Our cell phones, too, use GPS to track us. As the ACLU writes, “While virtually all of the roughly 250 police departments that responded to our request said they track cell phones, only a tiny minority reported consistently obtaining a warrant and demonstrating probable cause to do so.”

And that location tracking, sometimes using precise GPS coordinates communicated by our cell phones, is extensive – even apart from the automated-datamart vacuum operations at NSA we are discussing this week. US Congressman Ed Markey found that law enforcement filed over one million requests for cell phone records in 2011 — a number of requests that most likely implicated the private information of many more millions of people.

And these records can reflect years of our private habits and lives. The ACLU reports: “According to the U.S. Department of Justice, Sprint keeps location tracking records for 18-24 months, and AT&T holds onto them "since July 2008," suggesting they are stored indefinitely.”

Two years and indefinitely are certainly longer than the 31 days the Massachusetts Supreme Judicial Court found was “extended” in the Rousseau case.

But that’s not all.

Automatic license plate readers are increasingly compiling detailed records of everywhere motorists drive. Law enforcement at every level and even private corporations are hoarding this information in regional and even national databases. As the plate readers become cheaper and eventually ubiquitous, hanging from every intersection and attached to every police car, it’s a very real possibility that police will be able to track our every motoring move, going back months, years or even decades. In such cases, officers don’t even need to subpoena anyone for records, because they already have them.

That’s also the case with cell phone sniffing gear like the Stingray, which allows law enforcement to independently track our devices, cutting out the telecoms entirely.

As Supreme Court Justice Sonia Sotomayor wrote in a concurring opinion in the landmark Fourth Amendment case US v Jones,

GPS monitoring generates a precise, comprehensive record of a person's public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations. The Government can store such records and efficiently mine them for information years into the future. And because GPS monitoring is cheap in comparison to conventional surveillance techniques and, by design, proceeds surreptitiously, it evades the ordinary checks that constrain abusive law enforcement practices: "limited police resources and community hostility."

Sotomayor’s concerns pertain equally to location tracking by way of mobile phone, physical GPS device, and stored automatic license plate reader data.

Citing Jones, the Rousseau decision in Massachusetts makes clear that law enforcement in this state cannot use GPS to track us for an “extended” period of time unless they show probable cause to a judge. That ruling applies to GPS tracking in cell phones. It arguably also applies to detailed license plate reader databases, some of which already contain hundreds of millions of records showing where we drive, and when. These databases are only set to grow, and the vast majority of states have set no limits on how long police departments are allowed to store our location information.

Right now you may be thinking: ‘Who cares about whether or not the SJC said the cops need probable cause to spy on me like this? The NSA is already doing it!’ This is obviously a serious concern and we need to stop it. But the Rousseau decision still matters for people in Massachusetts, in a very big way.

That’s because, even if the Boston or Massachusetts State Police got access to NSA records showing where you went or for how long, they most likely wouldn’t be able to use that evidence against you in a Massachusetts court. Furthermore, the NSA probably isn’t in the business of sharing its preciously hoarded information with state and local police officers, except in highly extraordinary circumstances.

Even more importantly, many of us live in communities wherein we know people who work at the local prosecutors’ office, or are police officers. Local law enforcement is much more integrated into our lives than is the secretive, shadowy NSA. Therefore suspicionless, unaccountable surveillance at the local level poses unique threats to the sanctity of our lives, our dignity as private persons, and even our physical safety.

At the federal level, we need to repeal the FISA Amendments Act so that the military cannot routinely collect and store our private communications, associations and habits. But state law is incredibly important, as well.

That’s why we here in Massachusetts are working to pass legislation to deal with both warrantless cell phone tracking and unregulated license plate tracking, which we hope will become law sooner rather than later. (Join us and add your voice.)

Legislatures have a way of moving very slowly, however, and so in the meantime it’s heartening to see that our state’s highest court agrees on a basic principle, the violation of which underlies the entire NSA and PRISM scandal: if the police want to track our movements over an “extended” period of time, they need to have individualized suspicion and probable cause, and show that evidence to a judge.

It sounds almost quaint this week, but that’s how we do in Massachusetts.