Laser Beam Eavesdropping

Laser Beam Eavesdropping

History & Technology Explained

In 1988, newspaper reports about laser beam eavesdropping swept the country. Our clients were scared, and many others still are today. To learn exactly how scared they should be, we built a laser beam eavesdropping system and conducted a series of experiments. The following report to clients is the result of those experiments.

Since then, more research has been done. Hardware and techniques have improved. We traced the fascinating history behind laser beam eavesdropping back to April 26th, 1880 – Alexander Graham Bell & Sumner Tainter announce their invention – the Photophone. Sound is transmitted on reflected light-rays a distance of 213 meters. They also claim, “it can transmit songs with great purity of tone.” This is the forerunner of CDs, DVDs, fiber optic telephone transmission, and remote eavesdropping.

While laser beam eavesdropping is not entirely practical yet as an everyday amateur or business-level spy tool, advancements are being made. Last year, researchers from Bar-Ilan University (Ramat-Gan, Israel) and the Universitat de València (Burjassot, Spain) developed a new way to sense sound remotely using a laser beam.

Eavesdrop from afar, merely by pointing at a window. The idea is alluring to some, horrific to others.

News media reports of just such a bugging device, based on laser beam technology, have been circulating for some time now. A litany of claims “…can hear from miles away,” and compound-claims “…through closed windows…”

Sound is transmitted by vibration. When you speak, you vibrate the air. The air, in turn, vibrates everything it contacts. Certain objects, eg. windows and mirrors, pick up vibrations very easily. When a laser light beam hits such an object, it vibrates also as it reflects and continues its trip. The reflected, vibrating beam can be received; electronically processed; and then listened to. Under controlled conditions, very high quality audio can be recovered.


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