It is well-known that sound permeates through walls, doors, water, windows and other constructions as well as through voids, cavities and ventilation shafts. This property of materials makes it possible to intercept conversations conducted within a premises with the help of highly sensitive contact microphones (electronic stethoscopes), window laser systems or conventional microphones without entering the target area.
Wall contact microphones can pick up vibrations from the plumbing, structures, walls, windows, doors, floors, ceilings and more. The listening device may be in an adjacent room, or even several floors or rooms away attached to a wall, pipe or other fixture. Cavities such as air ducts, ventilation shafts or other voids can be used for intercepting sound from an adjacent premises with a help of conventional microphones.
