The History of Listening Devices


In 1946, a group of Soviet schoolchildren presented then U.S. Ambassador to the Soviet Union Averell Harriman with a wooden 2-foot replica of the Great Seal of the United States.The artifact hung inside the ambassador's office at the U.S. Embassy until in 1952, a security check revealed that a very ingenious listening device--a "bug"--had been inserted inside the replica. Any sound in the room caused a tiny spring to vibrate. Eavesdroppers outside the premises could then measure the vibrations and transform them into sound.


  • The term "listening device" generally applies to two types of electronic appliances: assistive listening devices for the hearing impaired, and those that are intended for overhearing or recording conversations. For the hearing impaired, assistive listening devices improve hearing through the amplification of sound. Such gadgets include hearing aids and magnetic induction loops. Devices used covertly are often referred to as bugs. These consist of microphones and radio transmitters.

Hearing Aids

  • The first assistive listening devices were implemented by simply placing an open hand behind one's ear, thus potentially magnifying sound waves by up to 12 decibels. Throughout history various cultures made use of ear trumpets, which consisted of sea shells, animal horns or wooden and metallic objects that were wide on one end but narrowed toward the ear piece. Experimentation with electronic appliances began in the 1890s, but they remained somewhat impractical until the invention of the transistor made portable hearing aids convenient during the 1950s. The following decades saw even more technological advancement.

Covert Devices

  • Before the existence of electronics, covert-listening devices consisted of little more than ear-size tubes or cylinders that were simultaneously placed against a wall and the ear, thus producing some sound amplification due to the vibrations in the wall. The first known electronic-snooping device was invented in 1945 by Léon Theremin. This was the Great Seal bug that is described above. Since that time, covert-listening devices have become much more advanced, often incorporating laser or infrared technology and no longer needing to be on the premises. Police undercover operations often include wiring their operatives with hidden microphones, thus enabling a remote recording of evidence.

Phone Taps

  • Law enforcement agencies have long been able to perform wire taps--listening to land-based telephone conversations. These are usually performed at the telephone companies providing the service. Today, with the advancement of cellular technology, government and police agencies use highly sophisticated methods of listening to such communications. This is often accomplished through the use of interceptors and recording devices.

Magnifying the Undetectable

  • The bionic ear sound amplifier is a somewhat covert device that is available commercially, enjoys a moderate degree of popularity and employs newly acquired technology. Sometimes used by birdwatchers and other nature observers, this device consists of headphones, a microphone and a sound amplifier that looks somewhat like a satellite dish. It is capable of augmenting faint sounds by 40 decibels from up to 100 yards away.


  • Since the mid-20th century, electronic technology has increased the usefulness and effectiveness of listening devices exponentially for the hearing impaired, law enforcement, covert government operations and nature lovers. Covert eavesdropping on private conversations, however, should only be performed by authorized police or government agents, as such activities are illegal for all others.

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