What Is It?
Every cell phone generates cell site location information (CSLI) every time it sends and receives electronic communications—such as calls, texts, emails, or web browsing—via its cellular network. This data is even generated when the phone is merely switched on and not actively exchanging these communications.
In order for a cell phone to work—to send and receive data—it must connect with a cell tower. Every time it does, it generates location information stored by the cell phone company about which cell tower the phone connected to—essentially a localized area where the phone was at the time of connection. These discrete data points are aggregated by cellular providers and, like Global Positioning System (GPS) data that may be stored on the phone itself, “generate a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations.” United States v. Jones, 132 S.Ct. 945, 955 (2012) (Sotomayor, J., concurring).
However, different phones have different capabilities. For example, modern phones have internal GPS receivers that also record location information. This is separate from CSLI, which is generated by the phone’s interaction with cell towers themselves. Traditional CSLI is a record of what cell towers the phone connected to and when, rather than where the phone actually is. Some cellular providers can attempt to locate a user’s cell phone in an emergency by “pinging” it—forcing the cell phone to connect to the nearest cell towers, even when it is not actively receiving or transmitting data, in order to measure the time it takes for the signal to travel from the cell phone to the cell tower and vice versa and extrapolate an approximate location for the device.
CSLI: Cell Site Location Information is a record of the location of the cell towers that a cell phone connected to at specific moments in time, and associated technical data.
GPS: The Global Positioning System network consists of about 30 satellites orbiting the Earth that broadcast radio signals down to the Earth’s surface. Each satellite transmits information about its position and the current time at regular intervals. These signals are received by a cell phone’s GPS receiver, which calculates how far away each satellite is based on how long it took for the messages to arrive. Once it has information on how far away at least three satellites are, the GPS receiver can determine the phone’s location with varying precision. This technology enables people to get directions from a variety of apps, and it’s the same technology that many other apps use for location-based recommendations, like tips for nearby restaurants or local weather predictions.
Historical Location information: Location information collected in the past (prior to the time of a data request), whether that was one day ago, one month ago, one year ago or beyond.
Prospective Location information: Current or future location information. Also referred to as “real-time” location information that live-tracks a cell phone’s location at any given moment.
Ping: another word for “contact” or “connect.” “Pinging” means to send a signal to a particular cell phone and have it respond with the requested data, typically revealing location data for the cell towers it used to connect to the cellular network.
Stored Communications Act (SCA): a law regulating how the government may access certain types of electronic communications data.