Covert listening device

A covert listening device, more commonly known as a bug or a wire, is usually a combination of a miniature radio transmitter with a microphone. The use of bugs, called bugging, or wiretapping is a common technique in surveillance, espionage and police investigations.
Self-contained electronic covert listening devices came into common use with intelligence agencies in the 1950s, when technology allowed for a suitable transmitter to be built into a relatively small package. By 1956, the U.S. Central Intelligence Agency was designing and building "Surveillance Transmitters" that employed transistors, which greatly reduced the size and power consumption. An all solid-state device had low enough power needs that it could be operated by small batteries, which revolutionized the business of covert listening.
A bug does not have to be a device specifically designed for the purpose of eavesdropping. For instance, with the right equipment, it is possible to remotely activate the microphone of cellular phones, even when a call is not being made, to listen to conversations in the vicinity of the phone.
Dictograph.
Among the earliest covert listening devices used in the United States of America was the dictograph, an invention of Kelley M. Turner patented in 1906 (US Patent US843186A). It consisted of a microphone in one location and a remote listening post with a speaker that could also be recorded using a phonograph. While also marketed as a device that allowed broadcasting of sounds, or dictating text from one room to a typist in another, it was used in several criminal investigations.
A wire.
A "wire" is a device that is hidden or concealed under a person's clothes for the purpose of covertly listening to conversations in proximity to the person wearing the "wire". Wires are typically used in police sting operations in order to gather information about suspects.
The act of "wearing a wire" refers to a person knowingly recording the conversation or transmitting the contents of a conversation to a police listening post. Usually, some sort of device is attached to the body in an inconspicuous way, such as taping a microphone wire to their chest. "Wearing a wire" by undercover agents is a typical plot element in gangster and police related movies and television shows. A stereotypical scene might include an individual being suspected by criminals of "wearing a wire", resulting in their tearing the suspect's shirt open to reveal the deception.
When infiltrating a criminal organization a mole may be given a "wire" to wear under their clothes.
The wire device transmits to a remote location where law enforcement agents monitor what is being said. Wearing a wire is viewed as risky since discovery of a hidden wire by a criminal could lead to violence against the mole or other retaliatory responses.
Remotely activated mobile phone microphones.
Mobile phone (cell phone) microphones can be activated remotely, without any need for physical access. This "roving bug" feature has been used by law enforcement agencies and intelligence services to listen in on nearby conversations. A United States court ruled in 1988 that a similar technique used by the FBI against reputed former Gulfport, Mississippi cocaine dealers after having obtained a court order was permissible. Not only microphones but also seemingly innocuous motion sensors, which can be accessed by third-party apps on Android and iOS devices without any notification to the user, are a potential eavesdropping channel in smartphones.
Automobile computer systems.
In 2003, the FBI obtained a court order to surreptitiously listen in on conversations in a car through the car's built-in emergency and tracking security system. A panel of the 9th Circuit Court of Appeals prohibited the use of this technique because it involved deactivating the device's security features.
Audio from optical sources.
A laser microphone can be used to reconstruct audio from a laser beam shot onto an object in a room, or a window.
Researchers have also prototyped a method for reconstructing audio from video of thin objects that can pick up sound vibrations, such as a houseplant or bag of potato chips.
Listening devices and the UK law.
The use of listening devices is permitted under UK law providing that they are used in compliance with Data Protection and Human Rights laws. If a government body or organisation intends to use listening or recording devices they must follow the laws put in place by the Regulation of Investigatory Powers Act (RIPA). It is usually permitted to record audio covertly in a public setting or one's own home.
Legal requirements of listening and recording device use.
It is illegal to use listening or recording devices that are not permitted for public use. Individuals may only use listening or recording devices within reasonable privacy laws for legitimate security and safety reasons. Many people use listening devices in their own property to capture evidence of excessive noise in a neighbour complaint, which is legal in normal circumstances.
Legal use of listening and recording devices.
It is legal to use listening or recording devices in public areas, in an office or business area, or in one's own home. Many people use listening devices to record evidence or even just to take notes for their own reference.
Illegal use of listening and recording devices.
It is illegal to use listening devices on certain Military band and Air Band UHF and FM frequencies - people in the past who have not followed this law have been fined over £10,000. This is because the use of a radio transmission bug that transmits on restricted frequencies contravenes the Telecommunications Act and is illegal. It is also against the law to place a listening or recording device in someone else's home. Due to privacy and human rights laws, using a listening or recording device to intrude on the reasonable expectation of privacy of an individual is highly illegal, i.e. placing gadgets in someone's home or car to which one does not have permitted access, or in a private area such as a bathroom.