From ScotusBlog: Digital location data heads back to the Supreme Court

The Supreme Court heard oral arguments Monday on "geofence warranting." 

- Click here for the article.

On Monday, April 27, the Supreme Court will hear Chatrie v. United States, a case about police access to geofence data, a digital record of a person’s location. This case could serve as a landmark intervention in Fourth Amendment doctrine in the digital age – or a more limited adjustment of those rules. The court could also greenlight or restrain “reverse” searches, a key investigative tactic of the digital age. Either way, this is the most important case on digital privacy the court has heard in years.

The Supreme Court last weighed in on the digital Fourth Amendment in 2017. In Carpenter v. United States, the court addressed whether the police had to get a warrant before accessing a certain kind of digital location data, cell-site location information. Cell phones generate CSLI anytime they are on by scanning for the nearest cell tower with strong service. When a cell phone connects to a tower, that tower then records that connection in CSLI logs. A phone’s location can be tracked across time and space by reviewing those logs.

Writing for a 5-4 majority, Chief Justice John Roberts’ Carpenter opinion held that the police must get a warrant before reviewing seven or more days of CSLI for a person’s phone. According to the court, reviewing that amount of location data without a warrant violates a person’s “reasonable expectation of privacy,” which is the legal threshold the court uses to determine whether constitutional protections kick in. The court also enumerated several factors that can be used to measure one’s reasonable expectations of privacy, such as how much the data reveals about a person, the amount of data gathered, and whether the user voluntarily generated the data.

Although Carpenter expanded Fourth Amendment protections for digital location, lower courts have spent the last decade contending with its boundaries.

Among these unsettled questions is whether police need a warrant to access geofence data, another kind of digital location data. Geofence data generally refers to location information collected by cellphone apps. If you have encountered a prompt on your phone that asks you whether you’d like to allow an app to use your location, you’re likely generating the kind of data at issue in Chatrie. Chatrie specifically involved data generated by a Google service called Location History. In Google’s case, this location information was created by combining information from cell towers but also on GPS, Wi-Fi, and Bluetooth signals.

In Carpenter, police sought location information about a particular suspect. But the geofence data in Chatrie is useful in a different situation – when the police have no suspect identified. Police can request information from a private company holding app location data for a list of users at a certain location during a certain timeframe to generate leads.

For more: 

- What is a geofence?

- What is a geofence warrant?

- Oyez: Chatrie v. United States.

- ScotusBlog: Chatrie v. United States.