Warrantless tracking by police using a person's cell phone or other personal device is being banned by a growing number of states in the latest legislative battle against government snooping.
Three states -- Indiana, Maine and Montana -- have already limited police use of cell phone signals to track a person's movements without a search warrant. Bills to curtail the practice are moving through 15 other state legislatures, according to a list from the American Legislative Exchange Council.
The bills are in part a response to the domestic surveillance done by the National Security Agency and the disclosures of former NSA contractor Edward Snowden, said John Stephenson, director of ALEC's task force on communications and technology.
But the court in that case specifically addressed the need for a warrant to attach a GPS tracking device. Left unanswered is whether following a person using a signal from cell phone or other personal device constitutes an illegal search.
“Since the mobile revolution started, much more information is available and accessible, and people are starting to grow concerned, particularly about the government’s access and use of such information,” Stephenson said. “The flood of interest in this really took off after the Snowden revelations. Suddenly people started asking questions about who has access to their data, who can get at it, what can the government do with it?”
Congress has done little to limit government surveillance. So states have taken up the issue, Stephenson said.
While the bills differ from state to state, they generally require police to obtain a search warrant in order to track signals from personal devices. Some go further. Indiana, for instance, also will ban the use of unmanned aerial drones to follow someone without a warrant in most circumstances starting July 1.
Maine and Montana were the first states to impose limits legislatively. Bills to limit the warrantless surveillance are supported by groups ranging from the conservative ALEC to more liberal American Civil Liberties Union.
Police would still be able to use personal devices to track someone under the proposals. But they would first have to obtain a search warrant establishing probable cause that the target committed a crime. That is consistent with the Fourth Amendment prohibition against unreasonable searches and simply applies those protections to the new technology, said Alan Butler, appellate advocacy counsel at the Electronic privacy Information Center, a nonprofit group that supports government transparency and personal privacy.
Though the laws would not apply to federal agencies, they would limit warrantless tracking by state and local agencies where the bulk of law enforcement work is done. They also send a signal to Congress, Butler said.
“This is a significant change in the process that law enforcement uses to conduct investigations, to do surveillance,” Butler said. “But it’s certainly not a sea change in the sense that it’s not limiting their ability to do the important work they need to do.
“Law enforcement obtains probable-cause warrants routinely in criminal investigations,” Butler said. “You are not prohibiting them from using this tool. You are just restricting the use of the tool to circumstances [in which] they’ve already identified probable cause.”
USA Today reported in December that dozens of state and local police are using new technologies that tap into cell phone signals in real time to capture information on thousands of cell phone users, not just those who are suspected of committing crimes.
About one in four law enforcement agencies reviewed by USA Today have used a tactic known as a "tower dump," which gives police data about the identity, activity and location of any phone that connects to the targeted cellphone towers over a set span of time, usually an hour or two.
A typical dump covers multiple towers and wireless providers, and can net information from thousands of phones.
Some police agencies also use a device called a Stingray, which tricks all nearby phones into connecting to it and feeding data to police.