Beware of light bulbs revealing your secrets

Over the years, various monitoring technologies have emerged one after another, such as wired bugs, telephone monitoring, wall holes, and even laser light reflected from the glass walls of buildings to monitor the conversations of people in the building. And now, another tool for monitoring sound comes out-the light bulb in the room.

Recently, researchers from the Weizmann Institute of Science and Ben Gurion University of the Negev in Israel disclosed a set of tools for long-distance monitoring, which they called “light machines.” With a laptop computer and equipment for less than $1,000 (a telescope and a set of electro-optical sensors for $400), as long as the sound causes the light bulb in the house to sway very little, anyone can identify the person in the house from hundreds of meters away in real time. The content of the conversation, or hear what music they are playing.

Penn Nasi, a security researcher at Ben Gurion University of the Negev in Israel, who invented this new technology, said: “You don’t need to place any equipment in the house, you can listen to the sound inside, just stare at the light inside the house.” Penn Nasi and colleagues Aaron Pirutin and Boris Sadov also presented their invention at the Black Hat Security Conference in August 2020. However, due to the special circumstances this year, the Black Hat Security Conference was held online. Researchers and developers used the chat platform to introduce their security products to people through video. According to the overseas edition of “Personal Computer” magazine, the bulb monitoring technology is one of the most feared products at this year’s Black Hat Security Conference.

In many experiments, the researchers used multiple electronic telescopes at a distance of 25 meters to aim the light bulbs in the target office, and an electro-optical sensor was connected in front of the eyepiece of each telescope. Then, they used an analog-digital converter to convert the signal received by the electro-optical sensor into a digital signal. When music or speech recordings are being played in a distant room, they can input the collected information into their laptop computers to analyze what music is being played and what the speech is. In the experiment, the researchers successfully reproduced the Beatles song “Let it be”.

However, this technology undoubtedly has limitations. In the experiment, the researchers used suspended light bulbs. If it is a light bulb fixed on the ceiling, the vibration will not be so obvious and it will not be possible to obtain so many sound signals. In addition, the Beatles songs they used to demonstrate were louder than people’s normal speech. However, the researchers also said that they use relatively inexpensive electro-optical sensors and analog-to-digital converters. If they want to get a smaller sound, they can upgrade these devices.