This blog hasn't been short on discussing a device that mimics a cell phone tower, but also tracks a person and obtains information from their phone. We discussed prior opinions related to this stingray technology in the federal circuits, where courts were faced with the intersection of these devices and the 4th Amendment, but ruled on other grounds.
Last month, the D.C. Court of Appeals took this issue on headfirst, ruling that the use of this device without a warrant violated the 4th Amendment. The court took a strong line on privacy and cell phones, holding that ruling otherwise "would also place an
individual in the difficult position either of accepting the risk that at any moment
his or her cellphone could be converted into tracking device or of forgoing
―necessary use of‖ the cellphone."
The court concluded that allowing such a search without a warrant would violate an individuals "actual, legitimate, and reasonable expectation of privacy in his or her location information and is a search."
There is a good discussion of Katz and the oft-made government argument that using a cell phone holds the information out to the public which is adverse to an expectation of privacy claim. Describing the distinction as a probabilistic one (whether the public thinks it is likely the government could access the information) v. a normative one (whether our history and tradition says the government should have access to this information).