Our friend at FourthAmendment.com has the text of an opinion from the Southern District of Texas about the ability of law enforcement to access cell site data
In this decision, the court acknowledged that "caselaw developments have been outstripped by advancing technology."
The court makes two main arguments in support of requiring a warrant.
First, the court suggests that the information is subject to constitutional protection because it can reveal information from inside a house. The court relies on the suggests that the information is subject to constitutional protection because it can reveal information from inside a house. The court relies on the Kyllo decision, in which the Supreme Court invalidated the use of thermal imagers to gather information from inside a home. I think this argument is not persuasive. The Kyllo Court held that the use of such devices without a warrant violated the Fourth Amendment because the devices were not readily available to the public and the devices revealed information about the interior of a residence that could not be obtained by the naked eye. The problem is that cell phone data is easily distinguishable from thermal imagers. Cell phones commonly, now, contain GPS tracking capability that is readily available to the public. For example, AT&T offers the ability to track the whereabouts of family iPhones.
I also believe that the emphasis on the interior of the home is less valuable in the electronic age, as more and more data is stored outside of the home by third parties.
Second, the court relies upon the recent Maynard decision involving GPS tracking. I have written about this decision a number of time. See here, here, and here on the blog, for example. For more details, see here for a draft of an article I am publishing on the topic this winter. Although the court finds that Maynard is "not essential" to its decision, it does find that it is "instructive, and provides additional support and alternative grounds for this decision." In Maynard, the DC Circuit held that the use of GPS tracking required a warrant because, even though the vehicle was visible by the public on the street at all time, the cumulative nature of the data obtained from the devices could reveal the type in intimate details about a person's life protected by the Fourth Amendment.
In fact, the court felt that the information from cell phones was more intrusive than the GPS device, because "the phone can be monitored indoors where the expectation of privacy is greatest. By contrast, the GPS device in Maynard revealed no information about the interior of a home or other constitutionally protected space."
Again, I think that the focus on indoor v. outdoors misses a bigger point. The better reason this information is protected by the Fourth Amendment, I believe, is that the disclosure of this information permits the type of sustained and long-term surveillance of a targeted individual, perhaps unrelated to any particular criminal action and likely to reveal intimate details about the person's life, is beyond the scope of a search permitted by other Fourth amendment cases.