Three bills in Congress would require warrants for mobile phone tracking, but the legislation hasn't moved forward.
The ACLU report shows "widespread confusion about what the law actually requires," Dempsey said.
Crump agreed, saying that in some cases, police are tracking the people who call the mobile phone of someone they are investigating. "That means if a suspected criminal calls his mother or orders a pizza, the police also track the mom and the pizza delivery person," she said. "A huge number of innocent people get swept up in the tracking, and that's not the sort of targeted and tightly controlled use of an invasive practice that ought to be in place."
The law about tracking mobile phones is "in a state of chaos," she added. "In some places police do get warrants and demonstrate probable cause," she said. "But in others, the police don't involve a court at all."
The U.S. Department of Justice has questioned the need for changes to ECPA, saying quick access to information such as mobile-phone tracking data can save lives.
The ACLU report also raises concerns about the length of time that mobile carriers retain customer location information. Verizon Wireless keeps records for one year, Sprint Nextel for 18 to 24 months, and AT&T has retained location data since July 2008, according to information supplied to the ACLU by one police department. That retention of data is not disclosed in privacy policies, the ACLU said.
Representatives of the three carriers did not immediately respond to requests for comments.
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