The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized. - 4th Amendment
The United States is "enter[ing] new and unchartered territory by breaking down traditional barriers between law enforcement and foreign intelligence." - Sen Patrick Leahy, 147 Cong Rec S10992 (daily ed. Oct 25, 2001)
In 1986, Congress caught up to technology by amending the Wiretap Act with ECPA. Pursuant to ECPA, officers may intercept the content of "electronic communications" where they have acquired a search warrant from a court and served it on a service provider where the content is to be intercepted. [18 U.S.C. § 2510(12)] [18 U.S.C. § 2516] [18 U.S.C. § 2518] [Rule 41] [Phonemaster] “Content” includes the subject line of emails; it does not include transactional information.
ECPA has three titles:
In enacting ECPA, Congress codified its understanding of computer networks at that time.
[Kerr p. 8 2004] Neither ECPA's statutory language nor its legislative history make any reference to the Internet. [Lupu 9] [Gellis 344] As a result, creating a clear picture of the new protections that ECPA brings is less than easy. Multiple federal courts, forced to apply ECPA in novel situations, have described ECPA as "famous (if not infamous) for its lack of clarity," [Steve Jackson Games 462 5th Cir. 1994] [Smith 1055 9th Cir. 1998 (stating that the 5th Circuit "might have put the matter too mildly")] that ECPA is "fraught with trip wires," and that it is "a fog of inclusions and exclusions." [Kerr, Lifting the “Fog” of Internet Surveillance (2003) (“The law of electronic surveillance is famously complex, if not entirely impenetrable.”)]
ECPA dramatically expanded the definition of “communications.” Previously wiretaps were of voice communications. ECPA expanded this to include non-voice communications including “signs, signals, writings, images, sound, data, or intelligence of any nature transmitted in whole or in part by wire, radio, electromagnetic, photoelectric or photo-optical systems.” [18 U.S.C. § 2510(12)] [H.R. Rep. No. 99-647 at 35 (commenting on definition of "Electronic Communications")] [Councilman (ECPA covers email including email in storage during transmission)]. If it’s out there, Congress wanted to reach out and touch it.
The 4th Amendment protects private conversations, Berger v. New York, 388 U.S. 41 (1967); Katz v. United States, 389 U.S. 347 (1967). It does not cloak information, even highly personal information, for which there is no individual justifiable expectation of privacy, such as telephone company records of calls made to and from an individual's home, Smith v. Maryland, 442 U.S. 735 (1979), or bank records of an individual's financial dealings, United States v. Miller, 425 U.S. 435 (1976). Statutory authority provides protections for those records.