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Eavesdropping is

[s]urreptitiously obtaining data from an unknowing end user who is performing a legitimate function. An example involves having a hidden sensor co-located with the legitimate sensor.[1]


Eavesdropping is

[p]assively monitoring network communications for data, including authentication credentials.[2]

Historical background[]

Although early American law proscribed common law "eavesdropping,"[3] the crime was little prosecuted and by the late nineteenth century had “nearly faded from the legal horizon.”[4] With the invention of the telegraph and telephone, however, state laws outlawing wiretapping or indiscretion by telephone and telegraph operators preserved the spirit of the common law prohibition in this country.

Congress enacted the first federal wiretap statute as a temporary measure to prevent disclosure of government secrets during World War I.[5] Later, it proscribed intercepting and divulging private radio messages in the Radio Act of 1927,[6] but did not immediately reestablish a federal wiretapping prohibition.

Olmstead v. U.S.[]

By the time of the landmark Supreme Court decision in Olmstead v. United States,[7] however, at least forty-one of the forty-eight states had banned wiretapping or forbidden telephone and telegraph employees and officers from disclosing the content of telephone or telegraph messages or both.

For a majority of the Olmstead Court, his Fourth Amendment challenge was doomed by the absence of “an official search and seizure of his person, or such a seizure of his papers or his tangible material effects, or an actual physical invasion of his house or curtilage for the purposes of making a seizure.”[8] Chief Justice Taft pointed out that Congress was free to provide protection which the Constitution did not.[9]

Communications Act of 1934[]

Congress responded to the Olmstead decision by enacting the Communications Act of 1934, which expanded the Radio Act’s proscription against intercepting and divulging radio communications to include intercepting and divulging radio or wire communications.[10]

Recording conversations[]

The Communications Act of 1934 outlawed wiretapping, but it said nothing about the use of machines to surreptitiously record and transmit face-to-face conversations.[11] In the absence of a statutory ban the number of surreptitious recording cases decided on Fourth Amendment grounds surged and the results began to erode Olmstead’s underpinnings.[12]

Erosion, however, came slowly. Initially the Court applied Olmstead’s principles to these electronic eavesdropping cases. Thus, the use of a dictaphone to secretly overhear a private conversation in an adjacent office offended no Fourth Amendment precipes because no physical trespass into the office in which the conversation took place had occurred.[13] Similarly, the absence of a physical trespass precluded Fourth Amendment coverage of the situation where a federal agent secretly recorded his conversation with a defendant held in a commercial laundry in an area open to the public.[14]

On the other hand, the Fourth Amendment did reach the government’s physical intrusion upon private property during an investigation, as for example when they drove a “spike mike” into the common wall of a row house until it made contact with a heating duct for the home in which the conversation occurred.[15] Silverman presented something of a technical problem, because there was some question whether the spike mike had actually crossed the property line of the defendant’s town house when it made contact with the heating duct. The Court declined to rest its decision on the technicalities of local property law, and instead found that the government’s conduct had intruded upon privacy of home and hearth in a manner condemned by the Fourth Amendment.[16]

Each of these cases focused upon whether a warrantless trespass onto private property had occurred, that is, whether the means of conducting a search and seizure had been so unreasonable as to offend the Fourth Amendment. Yet in each case, the object of the search and seizure had been not those tangible papers or effects for which the Fourth Amendment’s protection had been traditionally claimed, but an intangible, a conversation. This enlarged view of the Fourth Amendment could hardly be ignored, for "[i]t follows from . . . Silverman . . . that the Fourth Amendment may protect against the overhearing of verbal statements as well as against the more traditional seizure of papers and effects.”[17]

Katz v. U.S.[]

Soon thereafter the Supreme Court repudiated the notion that the Fourth Amendment’s protection was contingent upon some trespass to real property in Katz v. United States.[18] The Court in Katz held that the gateway for Fourth Amendment purposes stood at that point where an individual should to able to expect that his or her privacy would not be subjected to unwarranted governmental intrusion.[19]

Berger v. New York[]

One obvious consequence of Fourth Amendment coverage of wiretapping and other forms of electronic eavesdropping is the usual attachment of the Fourth Amendment’s warrant requirement. To avoid constitutional problems and at the same time preserve wiretapping and other forms of electronic eavesdropping as a law enforcement tool, some of the states established a statutory system under which law enforcement officials could obtain a warrant, or equivalent court order, authorizing wiretapping or electronic eavesdropping.

The Supreme Court rejected the constitutional adequacy of one of the more detailed of these state statutory schemes in Berger v. New York.[20] The statute was found deficient in its failure to require:

  • a particularized description of the place to be searched;
  • a particularized description of the crime to which the search and seizure related;
  • a particularized description of the conversation to be seized;
  • limitations to prevent general searches;
  • termination of the interception when the conversation sought had been seized;
  • prompt execution of the order;
  • return to the issuing court detailing the items seized; and
  • any showing exigent circumstances to overcome the want of prior notice.[21]

Title III of the Omnibus Crime Control and Safe Streets Act of 1968[]

Berger helped persuade Congress to enact Title III of the Omnibus Crime Control and Safe Streets Act of 1968,[22] a comprehensive wiretapping and electronic eavesdropping statute that not only outlawed both in general terms but that permitted federal and state law enforcement officers to use them under strict limitations designed to meet the objections in Berger.

A decade later another Supreme Court case persuaded Congress to supplement Title III with a judicially supervised procedure for the use of wiretapping and electronic eavesdropping in foreign intelligence gathering situations. When Congress passed Title III there was some question over the extent of the President’s inherent powers to authorize wiretaps — without judicial approval — in national security cases. As a consequence, the issue was simply removed from the Title III scheme.[23]

Foreign Intelligence Security Act of 1978[]

After the Supreme Court held that the President’s inherent powers were insufficient to excuse warrantless electronic eavesdropping on purely domestic threats to national security.[24] Congress considered it prudent to augment the foreign intelligence gathering authority of the United States with the Foreign Intelligence Surveillance Act of 1978 (FISA).[25] FISA provides a procedure for judicial review and authorization or denial of wiretapping and other forms of electronic eavesdropping for purposes of foreign intelligence gathering.

Electronic Communications Privacy Act of 1986[]

In 1986, Congress recast Title III in the Electronic Communications Privacy Act of 1986 (ECPA).[26] The Act followed the general outline of Title III with adjustments and additions. Like Title III, it sought to strike a balance between the interests of privacy and law enforcement, but it also reflected a congressional desire to avoid unnecessarily crippling infant industries in the fields of advanced communications technology.[27]

The Act also included new protection and law enforcement access provisions for stored wire and electronic communications and transactional records access (e-mail and phone records).[28] and for pen registers as well as trap and trace devices (devices for recording the calls placed to or from a particular telephone).[29]

Communications Assistance for Law Enforcement Act[]

In a more recent adjustment, the Communications Assistance for Law Enforcement Act (CALEA),[30] (inter alia), established a procedure designed to help police keep pace with telecommunications advances and to provide tighter protection for e-mail and cordless telephone communications. The current result of Congress’s legislative efforts, Title III/ECPA and related provisions, is an array of criminal prohibitions augmented by procedural schemes crafted to give government access to private communications in limited circumstances, ordinarily under judicial supervision.


  1. NSTC Subcommittee on Biometrics, Biometrics Glossary, at 10 (Sept. 14, 2006) (full-text).
  2. Information Security: Federal Agencies Have Taken Steps to Secure Wireless Networks, but Further Actions Can Mitigate Risk, at 8.
  3. At common law, "eavesdroppers, or such as listen under walls or windows, or the eaves of a house, to hearken after discourse, and thereupon to frame slanderous and mischievous tales, are a common nuisance and presentable at the court-leet; or are indictable at the sessions, and punishable by fine and finding of sureties for [their] good behavior." 4 Blackstone, Commentaries on the Laws of England 169 (1769).
  4. “Eavesdropping is indictable at the common law, not only in England but in our states. It is seldom brought to the attention of the courts, and our books contain too few decisions upon it to enable an author to define it with confidence. . . . It never occupied much space in the law, and it has nearly faded from the legal horizon.” 1 Bishop, Commentaries on the Criminal Law 670 (1882).
  5. 40 Stat. 1017-18 (1918)(“whoever during the period of governmental operation of the telephone and telegraph systems of the United States . . . shall, without authority and without the knowledge and consent of the other users thereof, except as may be necessary for operation of the service, tap any telegraph or telephone line . . . or whoever being employed in any such telephone or telegraph service shall divulge the contents of any such telephone or telegraph message to any person not duly authorized or entitled the receive the same, shall be fined not exceeding $1,000 or imprisoned for not more than one year or both”); 56 Cong. Rec. 10761-765 (1918).
  6. 44 Stat. 1172 (1927)(“[N]o person not being authorized by the sender shall intercept any message and publish the contents, substance, purpose, effect, or meaning of such intercepted message to any person. . . .”).
  7. 277 U.S. 438, 479-80 n.13 (1928) (Brandeis, J., dissenting). Olmstead is remembered most today for the dissents of Holmes and Brandeis, but for four decades it stood for the view that the Fourth Amendment’s search and seizure commands did not apply to government wiretapping accomplished without a trespass onto private property.
  8. 277 U.S. at 466.
  9. Congress may of course protect the secrecy of telephone messages by making them, when intercepted inadmissible in evidence in federal criminal trials, by direct legislation.” 277 U.S. at 465.
  10. 48 U.S.C. §§1103-04 (1934), 47 U.S.C. §605 (1940 ed.). The Act neither expressly condemned law enforcement interceptions nor called for the exclusion of wiretap evidence, but it was read to encompass both, Nardone v. United States, 302 U.S. 379 (1937); Nardone v. United States, 308 U.S. 321 (1939).
  11. Section 605 did ban the interception and divulgence of radio broadcasts but it did not reach the radio transmission of conversations that were broadcast unbeknownst to all of the parties to the conversation. Late in the game, the FCC supplied a partial solution when it banned the use of licensed radio equipment to overhear or record private conversation without the consent of all the parties involved in the conversation. 31 Fed. Reg. 3400 (Mar. 4, 1966), amending then 47 C.F.R. §§2.701, 15.11. The FCC excluded “operations of any law enforcement offices conducted under lawful authority.” Id.
  12. The volume of all Fourth Amendment cases calling for Supreme Court review increased dramatically after Mapp v. Ohio, 367 U.S. 643 (1961), acknowledged the application of the Fourth Amendment exclusionary rule to the states.
  13. Goldman v. United States, 316 U.S. 129 (1942).
  14. On Lee v. United States, 343 U.S. 747 (1952).
  15. Silverman v. United States, 365 U.S. 505 (1961).
  16. 365 U.S. at 510-12. “The absence of a physical invasion of the petitioner’s premises was also a vital factor in the Court’s decision in Olmstead v. United States . . . . In holding that the wiretapping there did not violate the Fourth Amendment, the Court noted that the insertions were made without trespass upon any property of the defendants. They were made in the basement of the large office building. The taps from house lines were made in the streets near the houses. 277 U.S. at 457. There was no entry of the houses or offices of the defendants. Id. at 464. Relying upon these circumstances, the Court reasoned that the intervening wires are not part of (the defendant’s) house or office any more than are the highways along which they are stretched. Id. at 465.
    Here, by contrast, the officers overheard the petitioners’ conversations only by usurping part of the petitioners’ house or office — a heating system which was an integral part of the premises occupied by the petitioners, a usurpation that was effected without their knowledge and without their consent. In these circumstances we need not pause to consider whether or not there was a technical trespass under the local property law relating to party walls. Inherent Fourth Amendment rights are not inevitably measurable in terms of ancient niceties of tort or real property law . . . .

    The Fourth Amendment, and the personal rights which it secures, have a long history. At the very core stands the right of a man to retreat into his own home and there be free from unreasonable governmental intrusion . . . This Court has never held that a federal officer may without warrant and without consent physically entrench into a man’s office or home, there secretly observe or listen, and relate at the man’s subsequent criminal trial what was seen or heard.

    A distinction between the dictaphone employed in Goldman and the spike mike utilized here seemed to the Court of Appeals too fine a one to draw. The court was unwilling to believe that the respective rights are to be measured in fractions of inches. But decision here does not turn upon the technicality of a trespass upon a party wall as a matter of local law. It is based upon the reality of an actual intrusion into a constitutionally protected area. What the Court said long ago bears repeating now: It may be that it is the obnoxious thing in its mildest and least repulsive form; but illegitimate and unconstitutional practices get their first footing in that way, namely, by silent approaches and slight deviations from legal modes of procedure. Boyd v. United States, 116 U.S. 616, 635. We find no occasion to re-examine Goldman here, but we decline to go beyond it, by even a fraction of an inch.

    365 U.S. at 510-12 (internal quotation marks omitted).

  17. Wong Sun v. United States. 371 U.S. 471, 485 (1963).
  18. 389 U.S. 347 (1967).
  19. Id. at 353.
  20. 388 U.S. 41 (1967).
  21. Id. at 58-60.
  22. 87 Stat. 197, 18 U.S.C. 2510-20 (1970 ed.).
  23. 18 U.S.C. §2511(3) (1970 ed.) (“Nothing contained in this chapter or in section 605 of the Communications Act . . . shall limit the constitutional power of the President to take such measures as he deems necessary to protect the Nation against actual or potential attack or other hostile acts of a foreign power, to obtain foreign intelligence information deemed essential to the security of the United States, or to protect national security information against foreign intelligence activities. . .”).
  24. United States v. United States District Court, 407 U.S. 297 (1972).
  25. 92 Stat. 1783, 50 U.S.C. 1801-11.
  26. 100 Stat. 1848, 18 U.S.C. §§2510-21.
  27. H.R. Rep. No. 647, 99th Cong., 2d Sess. 18-9 (1984); S. Rep. No. 541, 99th Cong., 2d Sess. 5 (1986).
  28. 100 Stat. 1860, 18 U.S.C. §§2701-10.
  29. 100 Stat. 1868, 18 U.S.C. §§3121-26.
  30. 108 Stat. 4179, 47 U.S.C. §§1001-10.


See also[]