The practice of intercepting others' wire, oral, or electronic communications by any means, typically without the consent or knowledge of the parties to the communications. At least since the mid-1880s, when telegraph and telephone communication were invented, people have found ways to intercept those communications by tapping the wires that carried the signal transmissions. And before telephones and telegraphs, neighbors leaned up against neighbors' walls to listen or peered through windows to peek. That long history of wiretapping notwithstanding, American courts did not consider its legality until the 1920s, when Roy Olmstead, an alcohol bootlegger, was convicted with evidence obtained in part from a wiretap of his telephone conversations. The U.S. Supreme Court upheld the constitutionality of the Olmstead wiretap because the conversations had been intercepted by investigators without physically entering Olmstead's property. Instead, the investigators had intercepted the conversations by tapping the wires outside Olmstead's property.

In the 1930s, Congress passed the first anti-wiretapping law, making wiretapping a crime and making evidence obtained by wiretapping inadmissible in court. By the 1960s, law enforcement had thought of a new twist: intercepting telephone conversations at public telephone booths by placing a transmitter that transmitted one side of the conversation to officers listening nearby. That method did not require that any wires be tapped. This issue came before the Supreme Court in the mid-1960s in Katz v. United States, a landmark opinion. In Katz, the Court held that physical intrusion into a protected space was not required to constitute Wiretapping; rather, interception of communications was illegal if the speaker had a reasonable expectation that the conversation was private—the so-called objective and subjective reasonable expectation of privacy principle. That two-pronged principle, that conversations and other tangible and intangible items were private as long as the person claiming the privacy had a subjectively reasonable belief it was private and that the privacy was of a type that society would objectively deem reasonable, continued for decades.

Shortly after the Katz opinion, Congress enacted Title III of the Omnibus Crime Control Act of 1968, which controls at the federal level interception of wire, oral, and electronic communications. Title III provides that wiretaps must be supported by a warrant, necessity, and probable cause, and must be executed only in relation to specific predicate acts, within a limited time and topic scope, and in a manner that minimizes the likelihood of intercepting communications beyond the target of the wiretap warrant:

Once granted, wiretap warrants are often referred to as T3 (Title III) warrants. Phone company personnel who assist in setting up a wiretap may not disclose the existence or target of that wiretap under penalty of federal criminal law. Assuming the phone calls intercepted in a T3 wiretap are otherwise relevant, the calls will be admissible in court as evidence. Note that civilians cannot obtain a T3 wiretap warrant.

Wiretaps are very difficult to obtain because of the very high standards and requirements of Title III, but once obtained, they are a font of prosecution evidence in a criminal case. Indeed, wiretaps should be supremely difficult to obtain. After all, the privacy of our conversations is a right we take seriously, and allowing law enforcement to listen to our calls without limits, requirements, or a warrant is exactly the sort of government intrusion the Fourth Amendment is intended to prevent.

T3 wiretaps are often executed in a listening center staffed by law enforcement officers around the clock. The minimization requirement renders wiretaps very personnel-intensive. The officers listen to intercepted calls in real time—as they are intercepted—listening for whether they must truncate the interception because nothing relevant to the investigation or the warrant has been intercepted. The officers work in shifts, each often assigned to listen to only a single line. When an investigation simultaneously taps multiple phones, the listening center is a very busy place. The listening officers write the time, date, calling phone number, dialed phone number, and topics on a tracking sheet that is passed to the listening center coordinators. Once the judge-approved deadline for the duration of the T3 wiretap has arrived, all interception ceases.

An interesting phenomenon, known as tickling the wire, occurs when officers, who are up on an active wiretap, feed critical but false information related to the crime at issue to the wiretapped persons in an effort to stimulate them to call accomplices and report that false information to them. Tickling the wire often stimulates conversations that are subsequently recorded via the T3 warrant. Whether tickling the wire is permissible has occasionally been litigated in pending criminal cases, but courts have not taken a consistent position on that issue to date.

When wiretapped evidence is offered in a criminal trial, the effect on the jury can be enormous. Although a criminal defendant cannot be compelled to take the witness stand and incriminate him- or herself, a criminal defendant can be compelled to sit at the defense table while his or her own words, on those recorded telephone calls, are played for the jury to hear. Long before those wiretapped conversations are played for the jury, however, the defendant's attorney has had an opportunity to try to suppress those recordings for lack of relevance, lack of proof of identity of the speakers, lack of adherence to the requirements of Title III, lack of proper procedures, among other challenges.

Wiretapping by law enforcement officers can be and often is conducted without any T3 warrant at all, in fact, without consulting any judge at all. If properly conducted, these warrantless wiretaps are perfectly permissible. Let's say that law enforcement officers are investigating a crime, and the victim has agreed to cooperate with the police in gathering evidence in the case. The officers ask the victim to place a call to the alleged perpetrator, and the victim agrees to do so. The victim also agrees to let the officers record both sides of the call that the victim places to the suspect. When the officers record a telephone call with the permission of at least one participant in that call, the officers need not have a T3 wiretap warrant. The officers need no wiretap at all. The logic is that no one engaged in a phone conversation with another person, even with a supposedly close friend or accomplice, has a reasonable expectation that the contents of that call will remain private. Even the best friend, spouse, or accomplice can have a change of heart and turn state's evidence at any point. Because the suspect has no reasonable expectation that the phone conversation will be private, the suspect has no Fourth Amendment right to have a warrant or probable cause support that interception. That call between the suspect and the victim, surreptitiously recorded by the police with the victim's cooperation and consent, is admissible in court against the suspect.

Of course, wiretapping is not always conducted by law enforcement officers. Rather, civilians, spouses, parents, and others sometimes set up devices to record others' conversations. Indeed, the Watergate scandal arose from an attempt to wiretap the offices of the Democratic National Committee headquarters in Washington, DC, an attempt that was later covered up by White House officials loyal to President Richard Nixon. If recorded without the permission of at least one participant in that intercepted conversation, that interception is illegal, as a violation of Title III.

But civilians can record, with impunity, any phone conversation to which they are a party. The theory is identical to the one allowing officers to have one party's consent to record a phone call. The person at the other end of a phone conversation has no reasonable expectation of privacy that the call will not be intercepted and recorded. An exception to this civilian rule applies to attorneys, whose ethical codes preclude them from recording telephone calls to which they are a party unless they give notice of the recording to the other parties to the call.

In sum, our telephone calls are private only if we have a reasonable expectation that they are private. When we place a call to or receive a call from someone we believe to be a friend, we are on notice that that person may be a false friend working with law enforcement. That is, we are aware that anyone can record their own telephone calls without notifying the other parties to the calls. Law enforcement officers can intercept and record telephone calls of others only if they have the consent of at least one party to do so or they have been granted a valid T3 wiretap warrant and abide by all its terms.

Note that Title III, by its terms, applies to wire, oral, and electronic communications. Wire communications include landline telephone calls and other communications transmitted by wires. Oral communications are conversations held by persons within hearing distance of each other. And electronic communications are those transmitted digitally or electronically, such as by cellular phone transmissions, Wi-Fi, or other similar electronic or digital means. Interception of any of these types of communications without consent of at least one party or without a T3 wiretap warrant is illegal. Any evidence seized by illegal means or beyond the scope of a T3 wiretap warrant is inadmissible and cannot be used as evidence in criminal court.

That rather exhaustive list of types of communications is, in reality, not exhaustive at all because many forms of communication do not fall within Title III's requirements. For example, if one has a conversation with another in a crowded restaurant, the parties have no reasonable expectation that the conversation will be private so that conversation is not protected from interception by Title III. Similarly, communications you transmit knowingly through a third person, such as notes on postcards or notes you hand to a third person for delivery to another, are not protected. Communications you send to multiple persons via email or text or post in public chatrooms on Twitter, Instagram, Facebook, and the like, are electronic communications, but they are not private and thus do not fall under Title III or require a wiretap warrant.

Some forms of communication are habitually nonprivate. At the most obvious extreme are cell phone calls, which cannot be completed unless the cell phone pings off a nearby cell tower. That ping tells the cell phone service provider, and anyone who asks the provider the right question, where that phone was and when, what numbers it called, what numbers called it, how long the calls lasted, and where the phone traveled from and when. Officers have increasingly used those cell phone pings, which they obtain through administrative subpoenas and stingrays (cell-site simulators controlled by law enforcement, commonly known as stingrays after the Harris Corporation's widely adopted stingray model), to track suspects in real time with no warrant, no probable cause, and no notice to the tracked person at all. In September 2015, the U.S. Department of Justice (DOJ) adopted regulations requiring its agents to obtain a warrant supported by probable cause and issued by a judge before using a cell-site simulator. Those DOJ regulations, which also allow warrantless use of cell-site simulators but only in exceptional circumstances, apply solely to DOJ's federal agents and not to state and local law enforcement officers. As the digital age progresses and makes communication simpler, it concomitantly reduces the privacy of those very communications.

Implications of these general principles are as follows:

Bear in mind that this essay was written with a focus on federal wiretap laws. State laws on interception and wiretapping of communications can very—and quite dramatically—from these federal rules. California law and the laws of up to eleven other states, for example, do not permit civilians, in most circumstances, to record a telephone call to which they are a party unless all parties to the call are notified or a distinct beep tone implicitly notifies all parties that the call is being recorded.

This essay deals with interception of the communications themselves, the words actually spoken. A much lower standard than T3 must be shown to intercept less detailed information such as numbers dialed, durations of telephone calls, and the like.

Further Reading

See also: Administrative searches; Cell phones; Electronic surveillance; Fourth Amendment to the U.S. Constitution; Katz v. United States; Olmstead v. United States; Privacy Laws, Federal; Privacy Laws, State; Smartphones; Telephones; USA PATRIOT Act