We've all heard a lot in the last month about the government's flimsy excuse for the NSA's massive collection of telephone and Internet metadata: that this sensitive information is somehow just "business records" that don't require a warrant for government access. That same argument has been used by the government to also justify the warrantless collection of cell site data -- the mobile company's record of which tower your phone connects to -- despite the fact that these records can reveal enormous amounts of information about where you go and with whom.

Thankfully, we're seeing some significant strides to put this dangerous idea to rest.

The New Jersey Supreme Court ruled this week that under the state's constitution police need a search warrant before tracking a person's location through their cell phone. This follows on the heels of a Massachusetts Supreme Judicial Court decision in June that found the state's constitution prohibited extensive GPS monitoring of an individual -- regardless of whether they are the driver or passenger of a car -- unless police obtained a search warrant. State legislatures are acting too; Montana recently became the first state to require police get a search warrant by statute before tracking a person's location (California had a chance to be the first state but Governor Jerry Brown vetoed the location privacy bill we sponsored last year). Massachusetts is considering similar legislation, and we submitted a support letter (PDF) encouraging them to do so. Maine recently passed a similar bill after the legislature overrode the governor's veto. And the New York Times reports over a dozen states are considering various electronic privacy bills.

Unfortunately, at the federal level there's still more work to be done. We joined the ACLU, the Center for Democracy and Technology and the National Association of Criminal Defense Lawyers in two recently filed amicus briefs before the Fourth and Eleventh Circuit Courts of Appeal, urging these federal courts to rule the Fourth Amendment prohibits warrantless cell phone tracking. We're still waiting for the Fifth Circuit Court of Appeals to issue its decision on the constitutionality of warrantless cell tracking in a case in a case we argued in New Orleans in October 2012. And there's federal legislation pending as well, with separate bills introduced by Senator Ron Wyden (S 639) and Representative Zoe Lofgren (HR 983) that would require a warrant before a person's location can be tracked through their cell phone or other electronic device.

With the growing use of cell data as a surveillance technique, coupled with new threats from technologies like license plate scanners and "stingrays," this judicial and legislative action is a step in the right direction towards ensuring the sensitive details surrounding our location aren't stripped of privacy protection merely because we ride in a car or use a cell phone.