FourthAmendment.com covers a decision out of the Southern District of Texas that held that cell phone location data is subject to the Fourth Amendment because it can reveal information from within the home.
From: In re Application of the United States of America for Historical Cell Site Data, 2010 U.S. Dist. LEXIS 115529 (S.D. Tex. October 29, 2010):
Conclusions of Law
A. Under Current Location Technology, Cell Site Information Reveals Non-Public Information About Constitutionally Protected Spaces
. . .
Even if an exact latitude and longitude is not yet ascertainable or recorded for every single mobile call, network technology is inevitably headed there. As the Supreme Court observed in Kyllo v. United States regarding the ongoing research and development of radar surveillance devices:
While the technology used in the present case was relatively crude, the rule we adopt must take account of more sophisticated systems that are already in use or development.
533 U.S. 27, 36 (2001). Like the thermal imaging devices in Kyllo, the cellular location technology in use or development today crosses the “firm but also bright” Fourth Amendment line that the Supreme Court has drawn at the entrance to the house. Id. at 40. Accordingly, the cell site records generated by that technology are subject to constitutional protection.
B. Historical Cell Site Records Are Subject to Fourth Amendment Protection under the Prolonged Surveillance Doctrine of United States v. Maynard
It is true that cell site records for a single day may not always reveal particularly intimate details about the user’s private life but merely that the user’s cell phone (like the Karo beeper) was present in the home at a particular time. Nevertheless, as Justice Scalia has observed, “[i]n the home, our cases show, all details are intimate details, because the entire area is held safe from prying government eyes.” Kyllo, 533 U.S. at 37 (emphasis in original). In this case, the records sought by the Government are likely far more intrusive — not a single snapshot at a point in time, but a continuous reality TV show, exposing two months’ worth of a person’s movements, activities, and associations in relentless detail.
In his decision denying warrantless access to historical cell site information, Judge Orenstein relied most heavily on the recent decision of the Court of Appeals for the District of Columbia in United States v. Maynard, 615 F.3d 544 (D.C. Cir. 2010). In light of the technological developments noted above, reliance on the Maynard precedent is not essential to the ruling here. Even so, Maynard‘s treatment of month-long GPS surveillance is instructive, and provides additional support and alternative grounds for this decision.
. . .
In several respects, the historical cell site records sought here are more invasive than the GPS data revealed in Maynard. The duration and volume of information sought is more than doubled — 60 days as opposed to 28 days of movement. As we have found, the level of detail provided by cell site technology now approaches that of GPS, and its reliability in obtaining a location fix actually exceeds that of GPS. 79 Moreover, as Judge Orenstein points out, cell phone tracking is likely more revealing than a GPS device attached to a car, because the cell phone is carried on the person. 80 It will also inevitably be more intrusive, 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.
Read more excerpts from the opinion on FourthAmendment.com