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, is a common technique in espionage and in police investigations.
Bug with transmitter
Most bugs use a radio transmitter
but there are many other options for carrying a signal: radio
frequencies may be sent through the main wiring of a building and
picked up outside; transmissions from a cordless phone can be
monitored; and it is possible to pick up the data from poorly
configured wireless computer
or tune in to the radio emissions of a computer
monitor or keyboard.
Bugs come in all shapes and sizes. The original purpose of bugs was
to relay sound, but today the miniaturization of electronics has
progressed so far that even commercially-available bugs designed to
carry TV signals are usually the size of a cigarette packet.
Professional bugs can fit into pens, calculators and other
commonplace items. Some are only the size of small shirt buttons,
although the power and operational life of the smallest bugs is
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
A panel of the 9th Circuit Court of Appeals
prohibited the use of this technique because it involved
deactivating the device's security features.
Remotely activated mobile phone microphones
(cell phone) microphones
can be activated remotely, without any need for physical access .
This roving bug feature is reportedly being used by law enforcement
agencies and intelligence services to listen in on nearby
conversations. A United States court ruled in 1986 that a
similar technique, used by the FBI against reputed former Gulfport Mississippi cocaine
dealers Bennett Branch and Don Tomlinson dealing cocaine under the
direct authority of kingpin David "The Eagle" Easterling after
having obtained a court order, was permissible.
While it is
not possible to do this with every
mobile phone as of
2006, some models are susceptible to being remotely reprogrammed
(over the air using methods meant for delivering upgrades (Firmware
updates and maintenance) with this capability without the knowledge
of its owner. Examples for such mobile phones are Motorola Razr and
Samsung 900 series mobile phones.
For the mobile phone as eavesdropping tool the OTA update function
is not used to transfer firmware or other official software but
rather "special" software which can offer one of the following
- The standard software user interface is manipulated or
overwritten in a way that phone calls which are done over the
infiltrated program are not shown.
- This special software is able to accept an incoming connection
(e.g. a call from a certain number) without showing this on the
mobile phone's user interface. This is possible as long as no
connection is existing at the same time.
- If the phone gets switched off the software only pretends this
(e.g. turning off the display). Incoming or outgoing connections
are still possible.
- Even though the mobile phone gets switched off, it is in a
standby comparable status. The "special" software is operating in
the background like the alarm clock function. Connection
establishment or answering a call in this status is already
For all mentioned points not only connection establishment of the
telephone lines needs to be considered. Also multi media functions
like bluetooth can be used for data transfer.
The person carrying the phone will not know that the phone is
transmitting his or her conversation, but an observant owner may
notice that the battery is being depleted sooner than
Instead of transmitting a conversation, bugs can instead record
Somebody can secretly record his conversation, or nearby
conversation, carrying a microphone and recorder. The microphone
and recorder can also be placed (mobile in an object or fixed), and
later either the whole set or just the recording carrier is
- Pocket sized devices, either worn or carried in baggage, linked
to a small microphone which is usually mounted on the surface to
pick up the audio. Digital devices such as minidisc recorders or
even mobiles or the latest palm-sized camcorders produce very high
quality recordings and are conveniently small.
- Larger recording devices hidden in the room, for example above
suspended ceilings. These are popular in workplaces for monitoring
Listening from a distance without radio transmission
- Ultra-directional microphones, or parabolic microphones. These are like
the microphones seen on camcorders, or carried by sound
technicians. They are constructed to receive signals only from one
direction. The most high-tech directional microphones can eavesdrop
on conversations from a hundred metres away or more. Microphone arrays can be used as well.
- Laser microphones. These are
very expensive and highly technical to operate. A laser beam is
bounced off a window, or off any object near to the conversation
monitored. Any object which can resonate/vibrate (for example, a
picture on a wall) will do so in response to the pressure waves
created by noises present in a room. The electronics detect the
minute difference in the distance travelled by the light to pick up
this resonance and reproduce the sound causing it. However, the
simple countermeasure of closing the curtains in a room radically
reduces the effectiveness of this surveillance method, assuming of
course that the laser beam originates from a source external to the
- Some equipment may exhibit microphonics and can therefore, unsuspected by
the party listened to, act as a microphone.
- The adversary can use a trojan horse to acquire access to
microphones connected to a computer.
- Telephone lines can be used as the transmission medium for
devices called "infinity transmitters" or "harmonica bugs". These
are covert listening devices connected either inside a target's
telephone or somewhere along the telephone line and activated by
calling the number. The circuitry silences the ringer long enough
for the eavesdropper to send a control tone that activates the
microphone. This allows surveillance to be conducted from anywhere
in the world, hence the name "infinity". With the advent of
remotely programmable mobile telephone technology (smartphones,
etc.), this technique can be used without having to plant anything.
Called "roving bugs", it involves the upload of surveillance
software to the target phone.
Most bugs emit radio waves. The standard counter-measure for bugs
is therefore to 'sweep' for them with a receiver, looking for the
radio emissions. Professional sweeping devices are very expensive.
Low-tech sweeping devices are available through amateur electrical
magazines, or they may be built from circuit designs on the
Internet. But sweeping is not foolproof. Advanced bugs can be
remotely operated to switch on and off, and some even rapidly
switch frequencies in order to make location with sweepers more
difficult. A bug that has run out of power may not show up during a
sweep, which means that the sweeper will not be alerted to the
surveillance. Burst transmitter bugs store recorded conversations
in a buffer, then transmit the entire buffer in a short burst. This
style of bug is almost impossible to pick up unless sophisticated
scanning devices are running nonstop.
Bugs that do not emit radio waves are much more difficult to
Examples of use
- Embassies and other diplomatic posts are
often the targets of bugging operations.
in Ottawa was bugged by the Canadian government
and MI5 during its
- Extensive bugging of the West German embassy in Moscow by the
discovered by German engineer Horst
Schwirkmann, leading to an attack on Schwirkmann in
- The Great Seal
bug was hidden in a copy of the Great Seal of the United
States, presented by the Soviet Union to the United States ambassador in Moscow in 1946 (not
discovered until 1952). The bug was unusual in that it had
no power source or transmitter, making it much harder to
detect — it was a new type of device, called a Passive Resonant Cavity Bug. The
cavity had a metallic diaphragm that moved in unison with sound
waves from a conversation in the room. When illuminated by a
microwave beam from a remote location, the cavity would return a
- The United States Embassy in Moscow was bugged during its
construction in the 1970s by Soviet agents posing as laborers. When
discovered in the early 1980s, it was found that even the concrete
columns were so riddled with bugs that the building eventually had
to be torn down and replaced with a new one, built with U.S.
materials and labor. For a time, until the new building was
completed, embassy workers had to communicate in conference rooms
in writing, using children's "Mystic Writing Tablets".
1990, it was reported that the embassy of the People's
Republic of China in Canberra, Australia, had been
bugged by the Australian Secret Intelligence
- Colin Thatcher,
a Canadian politician,
was secretly recorded making statements which would later be used
to convict him of his wife's murder. The recording device
was concealed on a person who Thatcher had previously approached
for help in the crime.
- Electronic bugging devices were found in
March 2003 at offices used by French and German delegations
at the European Union headquarters in Brussels. Devices were also discovered at offices
used by other delegations. The discovery of the telephone tapping systems was first
reported by Le Figaro newspaper,
which blamed the US.
- The car of Thomas Hentschell, who was involved in the Melbourne gangland killings, was
bugged by police.
1999, the US expelled a Russian diplomat, accusing him of using a
listening device in a top floor conference room used by diplomats
in the United States Department of
2001, the government of the People's Republic of China announced that it had discovered twenty-seven bugs
in a Boeing 767 purchased as an official
aircraft for President Jiang
- In 2003, Pakistani embassy building was found bugged,
contractors hired by MI5 planted bugs in the building in 2001.
- In 2003, Alastair John
Campbell (who was Director of
Communications and Strategy from 1997-2003 for UK PM) in his
memoirs The Blair Years: The Alastair Campbell Diaries
alleged that two bugs were discovered in the hotel room meant for
visiting British PM Tony Blair planted by
agencies.The alleged bug discovery was at a hotel during PM
Tony Blair's official visit to New Delhi in 2001. Security services
supposedly informed him that bugs cannot be removed without
drilling the wall and therefore he changed to another room.
2004, a bug was found in a meeting room at the United Nations offices in Geneva.
2008 it was reported that an electric samovar presented to Elizabeth II in about 1968 by a Soviet
aerobatic team was removed from Balmoral Castle as a security precaution amid fears that its wiring
could contain a listening device.