Spycraft - Melton [236]
Commercial microphones were developed in the latter quarter of the nineteenth century after Emile Berliner sold his microphone patent to the fledgling Bell Telephone Company. The world’s first electronic eavesdropping system, the Turner Dictograph introduced in 1915, contained a carbon microphone, battery, and earphone. Buyers were cautioned “not to use the device for illegal or immoral purposes.” Whether a microphone is located inside the mouthpiece of a telephone, or embedded in the wooden leg of a table, its purpose is the same—to convert the sounds of room noise and voices into an electrical signal.10
From the variety of microphones available, the techs matched the one with the most desirable characteristics to the operational requirement. Mics could be hardwired to the listening post, connected to a concealed recorder worn beneath the user’s clothing, or connected to a radio-frequency transmitter. While a hardwired mic offered security advantages, the radio-frequency transmitter quickly became the most commonly used audio system because the listening post could be placed in remote locations.
Contact microphones are effective in capturing sound waves from room audio that cause every hard surface in the room, including the walls, floors, and objects, to vibrate. A sensitive contact microphone with the capability to convert vibrations into an electric signal was especially useful in operations against targets in hotel rooms when the tech had physical access to one of the adjacent rooms, or the room above or below. The tech could affix the contact microphone to the wall or floor using glue or a nail to pick up the vibrations. A special type of contact microphone, the “accelerometer,” could detect vibrations of room conversation or movement through solid concrete walls up to eighteen inches thick. For opportunities that required quick reaction, OTS produced a special self-contained “motel kit,” disguised inside a small toiletries case, that consisted of a contact microphone, wall adhesive, pocket amplifier with optional output to a tape recorder, and earpiece.11 It could be packed in a briefcase or carried beneath a coat.
Illustrated are five different types of microphones intelligence services used for covert monitoring of conversations through a common wall. The degree of access to the target room and type of building construction determined which microphone was used.
The “vibro-acoustic” microphone, designed to be affixed to a reinforcing steel rod or bar inside a concrete column during building construction, could later be connected to concealed wiring that would run to a listening post. Conversations cause the concrete and rebar to vibrate and enable the vibro-acoustic sensor to capture the sounds. Multiple sensors inside the same column on different pieces of rebar could be selectively tuned by the monitor at the post to target specific conversations anywhere in a 360-degree circle around the column. However, the task of attaching the vibro-acoustic mics onto the rebar required bribing or distracting security guards at the construction site.
Pinhole mics, half the size of a pencil eraser, were a workhorse for the OTS audio techs. Whether mics were hidden behind a floorboard, inside a wall, or embedded in the base of a flowerpot, they required only a tiny (less than half a millimeter) airway to capture all of the room noises. The pinhole mic could be installed inside numerous objects or architectural features of a room. When denied access to the target room, the tech could install the mic in a common wall by drilling a pinhole too small to be noticed through the wall, floor, or ceiling.
TSD developed a “Motel Kit” for surveillance of targets