Commentators and Congress have long assumed that government surveillance of non-content “header” information like e-mail addresses and IP addresses, typically done by a service provider, do not violate a Fourth Amendment “reasonable expectation of privacy.” Today the Ninth Circuit became the first court to hold this directly in United States v. Forrester.
My major concern with this opinion is that, unless I’m missing something, the opinion does not actually say how the surveillance occurred. The Court states that the government used “a pen register analogue on [the defendant]