Indeed, the decision alone is a huge privacy win, but Sentelle's strong language supporting cell phone users' privacy rights is perhaps the most important part of the opinion. Sentelle pushed back against several of the federal government's arguments, including one that suggested that, because cell phone location data based on a caller's closest cell tower isn't precise, it should be readily collectable.
"The United States further argues that cell site location information is less protected than GPS data because it is less precise. We are not sure why this should be significant. We do not doubt that there may be a difference in precision, but that is not to say that the difference in precision has constitutional significance," Sentelle wrote. "That information obtained by an invasion of privacy may not be entirely precise does not change the calculus as to whether obtaining it was in fact an invasion of privacy."
The court also cited the infamous US v. Jones Supreme Court decision that held that attaching a GPS to a suspect's car is a "search" under the Fourth Amendment. Sentelle suggested a cell phone user has an even greater expectation of location privacy with his or her cell phone use than a driver does with his or her car. A car, Sentelle wrote, isn't always with a person, while a cell phone, these days, usually is.