Under the “third-party doctrine,” people give up their expectation of privacy when they share information voluntarily with a third party — like a wireless service provider. So instead of requesting a warrant based on the Fourth Amendment’s high “probable cause” standard, law enforcement was able to obtain records of Mr. Carpenter’s location after satisfying the lower standard of evidence federal legislation requires.
Congress passed that law in 1986 — before cellphones existed in their current form. Likewise, courts developed the third-party doctrine in the 1960s and ’70s. Under that legal regime, the government can now acquire much more invasive information than it was able to decades ago. It’s true that location records can vary in precision. But as Justice Sonia Sotomayor noted, that information may grow more and more accurate as technology continues to develop.
We’ve all been saying this for at least 20 years.