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Necktie bug
Professional covert radio bug

The Necktie bug was a professional crystal-based miniature covert transmitter built in the early 1990s by Mactron in Oosterbeek (Netherlands). The device was intended for body-worn use during covert and under cover operations, primarily by government agencies such as the police.
The Necktie bug received its name from the primary concealment it was intended for. It was designed to fit inside the knot of a necktie and was thought not to be discovered during a body search. A thin wire of approx. 30 cm, acting as the antenna, ran down the cloth of the necktie.

The unit was powered by a large 3V button-type CR-2430 lithium battery. The image on the right shows the prototype of the nectie bug. It is built inside a slim line metal enclosure with a separate compartment for the battery. The microphone with built-in pre-amplifier is at the front left.
Necktie bug (prototype)

During an investigation, law enforcement agencies sometimes use an under cover police officer or a 'turned' criminal as a bate, in the hope that the prime suspect reveals incriminating details that can be used as evidence during the investigation and in court. In such cases, the bate often carries a concealed transmitter and is then said to be 'wired' or to be 'carrying a wire'.
It allows nearby police officers to eavesdrop on the conversation whilst recording it, and take action if necessary. Carrying such a wire is not without risk. Criminals generally know they are being watched and will be extra careful when talking confidentially. In such cases, the wired person is likely to receive a body search.

The image on the right shows the transmitter nicely hidden inside the knot of a necktie. In this case the wire antenna is sewed behind the lining of the necktie, completely invisible to the naked eye, in such a way that it is lined up vertically.
The bug hidden inside the knot of a necktie

The microphone is located at the top of the knot, in the ideal position for picking up the conversation. Due to its rather high position on the human body and the well-constructed circuit, the necktie bug has a remarkably good operational range. In combination with a high-end communications receiver it was possible to cover a distance of more than one kilometer!
The transmitter is housed in a slimline metal case which is 37 x 37 mm in size and just 4 mm high. The image on the right shows the interior of the necktie bug in which only miniature and subminiature components are used. Most of the space is taken by the high-capacity 3V battery that allowed eight hours of uninterrupted use.

The small electret microphone is located at the front left. The frequency of the transmitter is determined by the crystal in the top corner, that is used in the 3rd overtone. This example works at a frequency of 154.050 MHz (51.350 x 3).
Interior of the necktie bug

The necktie bug was built in small quantities, exclusively for law enforcement agencies, intelligence agencies and private investigators, in The Netherlands and elsewhere. According to surviving eyewitness stories, the necktie bug was used in a number of high-profile undercover operations, but was never detected by criminals during a body search.
Necktie bug (prototype) Slimline necktie bug Opening the necktie bug Opened necktie bug and CR-2430 battery Interior of the necktie bug The necktie bug aside a normal necktie The necktie bug above the knot of a necktie The bug hidden inside the knot of a necktie

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Crypto Museum. Created: Monday 29 April 2013. Last changed: Friday, 13 January 2017 - 22:13 CET.
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