It’s quite crucial that the U.S. Supreme Court rule in favor of protecting privacy rights and rule against the antiquated third-party doctrine. People’s locations should not be automatically tracked by the government for simply having their phones on and with them.

Many cellphone users have only a vague understanding of the extent to which providers monitor their movements, but these companies now track us much more closely than even the most committed human spies ever could. Cellphones function by connecting to antennas – “cell sites” or “cell towers” – that provide cellular service. Those cell sites, which are owned and operated by the cellular companies, are programmed to record which phones connect to them, and when. They also record the direction from which the connecting phone’s signal is received and, often, the distance of the phone from the cell site.

So-called “cell site location information” is becoming ever more precise, because the cellular network is becoming ever more dense. The analytical tools that can be brought to bear on this information are also becoming more sophisticated, meaning that investigators can draw reliable conclusions from smaller and smaller amounts of data. It’s precisely because the information is so rich, of course, that the government is interested in accessing it.

Privacy scholars are watching Carpenter’s case closely because it may require the supreme court to address the scope and continuing relevance of the “third-party-records doctrine”, a judicially developed rule that has sometimes been understood to mean that a person surrenders her constitutional privacy interest in information that she turns over to a third party. The government contends that Carpenter lacks a constitutionally protected privacy interest in his location data because his cellphone was continually sharing that data with his cellphone provider.