Covert listening device - spy bugs, a topic that is usually revealed in detective novels and movies.

A hidden listening device, commonly known as a bug or wire, typically combines a miniature radio transmitter with a microphone. Bugs or wiretaps are widely used methods of surveillance, espionage, and police investigations.

Standalone electronic devices for covert listening became widespread in intelligence agencies in the 1950s, when technology allowed suitable transmitters to be embedded in relatively small cases. By 1956, the CIA was developing and producing “surveillance transmitters” using transistors, significantly reducing size and power consumption. These solid-state devices, with no moving parts and greater energy efficiency, could operate on small batteries, revolutionizing covert listening.

Listening doesn’t necessarily require a device specifically designed for eavesdropping on phone conversations. For instance, with the right equipment, a cell phone’s microphone can be remotely activated, even when not in use, to listen to nearby conversations.

DICTOGRAPH

One of the earliest covert listening devices used in the United States was the dictograph, invented by Kelley M. Turner and patented in 1906 (US Patent US843186A). It consisted of a microphone placed in one location and a remote listening post with a loudspeaker, which could also be recorded using a phonograph. Although advertised as a way to transmit sounds or dictate text from one room to a typist in another, it was used in several criminal investigations.

WIRE

A “wire” is a device hidden or disguised on a person to secretly listen to conversations happening nearby. Wires are typically used in undercover police operations to gather information about suspects. The listening device transmits the signal to a remote location where law enforcement officers monitor the situation.

The term “wire” refers to a person who knowingly records a conversation or transmits its content to a listening police post. Usually, some device is discreetly attached to the body, such as a microphone wire taped to the chest. Undercover agents wearing wires are a staple in gangster movies and police dramas. In stereotypical scenes, criminals may suspect someone of “wearing a wire,” leading them to rip off the person’s shirt to expose the deception.

When infiltrating a criminal organization, an undercover agent may be issued a “bug” to wear under their clothing.

Using a wire is considered risky, as discovery can lead to violence against the informant or other retaliatory measures.

Remotely Activated Cell Phone Microphones

Cell phone microphones can be activated remotely without any physical access. This “roving bug” feature has been used by law enforcement and intelligence agencies to eavesdrop on nearby conversations. In 1988, a U.S. court ruled that such a technique, used by the FBI against known former cocaine dealers in Gulfport, Mississippi, after obtaining a court order, was permissible. Not only microphones but also seemingly harmless motion sensors, which can be accessed by third-party apps on Android and iOS devices without user notification, are potential eavesdropping channels in smartphones.

Automotive Computer Systems

In 2003, the FBI obtained a court order to secretly listen to conversations in a car through its built-in security system. However, the Ninth Circuit Court of Appeals prohibited the use of this technology because it required disabling the device’s safety features.

Sound from Optical Sources

A laser microphone can convert sound into a laser beam aimed at an object inside a room or at a windowpane.

Researchers have also developed a prototype method to recover sound from video images of thin objects that can capture sound vibrations, such as a houseplant or a bag of potato chips.

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