Use of this type of location-tracking data by the government has not been tested in court. And in the private sector, location data — and the multibillion dollar advertising ecosystem that has eagerly embraced it — are both opaque and largely unregulated.

Last year, a Times Opinion investigation found that claims about the anonymity of location data are untrue since comprehensive records of time and place easily identify real people. Consider a commute: Even without a name, how many phones travel between a specific home and specific office every day?

This week’s revelations dredge up many questions about C.B.P.’s workflow: What precisely does the agency mean when it claims that the data is not ingested in bulk? Who in the agency gets to look at the data and for what purposes? Where is it stored? How long is it stored for? If the government plans to outsource the surveillance state to commercial entities to bypass Supreme Court rulings, both parties ought to be questioned under oath about the specifics of their practices.

The use of location data to aid in deportations also demonstrates how out of date the notion of informed consent has become. When users accept the terms and conditions for various digital products, not only are they uninformed about how their data is gathered, they are also consenting to future uses that they could never predict.

Without oversight, it is inconceivable that tactics turned against undocumented immigrants won’t eventually be turned to the enforcement of other laws. As the world has seen in the streets of Hong Kong, where protesters wear masks to avoid a network of government facial-recognition cameras, once a surveillance technology is widely deployed in a society it is almost impossible to uproot.

Chief Justice Roberts outlined those stakes in his Carpenter ruling. “The retrospective quality of the data here gives police access to a category of information otherwise unknowable. In the past, attempts to reconstruct a person’s movements were limited by a dearth of records and the frailties of recollection. With access to [cellphone location data], the Government can now travel back in time to retrace a person’s whereabouts, subject only to the retention polices of the wireless carriers, which currently maintain records for up to five years. Critically, because location information is continually logged for all of the 400 million devices in the United States — not just those belonging to persons who might happen to come under investigation — this newfound tracking capacity runs against everyone.”

The courts are a ponderous and imperfect venue for protecting Fourth Amendment rights in an age of rapid technological advancement. Exhibit A is the notion that the Carpenter ruling applies only to location data captured by cellphone towers and not to location data streamed from smartphone apps, which can produce nearly identical troves of information.