Third Party Doctrine limited as 4th Amendment protects CSLI
Interesting decision (at least for our friends in the US)
Cell phone users, by contrast, do not “voluntarily convey” their location to the cellular service provider in the manner contemplated by Miller and Smith. This is especially true when historical CSLI is generated just because the cell phone is on, such as when cell phone apps are sending and receiving data in the background or when the cell phone is “pinging” a nearby cell tower. As the government’s FBI special agent explained, “CSLI for a cellular telephone may still be generated in the absence of user interaction with a cellular telephone.” …. “For example,” the special agent continued, CSLI may be generated by “applications that continually run in the background that send and receive data (e.g. email applications).” … At oral argument, the government confirmed that its § 2703(d) application authorizes the government to obtain historical CSLI generated by such activities.
[….] In so doing, a cell phone periodically identifies itself to the closest cell tower—not necessarily the closest cell tower geographically, but the one with the strongest radio signal—as it moves through its network’s coverage area…. This process, known as “registration” or “pinging,” facilitates the making and receiving of calls, the sending and receiving of text messages, and the sending and receiving of cell phone data…. Pinging nearby cell towers is automatic and occurs whenever the phone is on, without the user’s input or control…. This sort of pinging happens every seven to nine minutes….
In Miller and Smith, the individual knew with certainty the information that was being conveyed and the third party to which the conveyance was made. Cell phone users, on the other hand, enjoy far less certainty with respect to CSLI. CSLI, in contrast to deposit slips or digits on a telephone, is neither tangible nor visible to a cell phone user. When the telephone user in Smith received his monthly bill from the phone company, the numbers he dialed would appear…. The CSLI generated by a user’s cell phone makes no such appearance…. Rather, because CSLI is generated automatically whenever a cell tower detects radio waves from a cell phone, a cell phone user typically does not know that her phone is communicating with a cell tower, much less the specific cell tower with which her phone is communicating…. It may be, as the government explained, that a cell phone connects to “many towers” during the length of a call,… and the tower to which a cell phone connects is not necessarily the closest one geographically…. Moreover, when an app on the user’s phone is continually running in the background, … she may not be aware that the cell phone in her pocket is generating CSLI in the first place.
In light of the foregoing, the Court concludes that historical CSLI generated via continuously operating apps or automatic pinging does not amount to a voluntary conveyance of the user’s location twenty-four hours a day for sixty days. Such data, it is clear, may be generated with far less intent, awareness, or affirmative conduct on the part of the user than what was at issue in Miller and Smith.