Researchers at Ben-Gurion University have described a new technique for eavesdropping on other people's conversations from a distance. To implement the method, a laptop, a telescope and an electro-optical sensor are sufficient. With this kit, you can distinguish sounds from a distance of hundreds of meters.
Ben Nassi and his colleagues at Ben-Gurion University have come up with a new technique of "visual eavesdropping" called Lamphone. The main idea of the method is that the researchers decided to use a light bulb as the object from which the vibrations caused by sound are removed - hence the name of the technique. The light bulb is an object as simple as possible and at the same time as bright as possible. Therefore, you can not waste computing resources on the analysis of the smallest details of the image. It is enough to direct a powerful telescope at the light bulb, through which the light flux from the light bulb enters the photocell.
The light bulb does not quite uniformly emit light in different directions (interestingly, this unevenness is not the same: it is quite high in incandescent and diode lamps, but much lower in fluorescent ones). Due to this unevenness, the vibrations of the light bulb caused by sound waves slightly change the intensity of the light flux in the direction of the photocell. And these changes are quite sufficient for them to be registered with confidence. By recording these changes and performing a number of simple transformations, the researchers were able to recover the sound from the resulting "light recording".
Details of the method are given on the website of the project of Israeli scientists. The wiretapping is carried out using an electro-optical sensor, which records the vibrations of a light bulb through the light from it; a telescope is used to transmit light. You can decrypt the received data on a regular laptop.
To test their device, the researchers set up a test site on a footbridge 25 meters from the office on the third floor in a commercial building. Their goal was a simple 12-watt LED light bulb, and by observing it, they were able to recreate the speech and music sounding inside the office.
To do this, they used three telescopes with different lens diameters - 10, 20 and 35 centimeters and installed an electro-optical sensor on each telescope lens for each session. Through an analog-to-digital converter, the researchers obtained information about the vibrations in the light bulb, and then processed it using a special algorithm. As a result, they got a recording of Trump's speech, which was able to recognize the Speech-To-Text API from Google, and a recording of "Let It Be" by the Beatles, which Shazam was able to recognize.
