Hackers Use Light Bulb to Eavesdrop on Conversations

The technique allowed them to spy on people from hundreds of feet away.
Derya Ozdemir

IoT has gained momentum, and the usual way of eavesdropping with a glass over the wall has come a long way: bugs in the wall, hacking weak passwords, wiretaps, and more. Now, as if there weren't enough ways of being an audio spy, the good old light bulb has become a nemesis to be feared: Any light bulb in a room that is visible from the window can be used to spy on your conversations from afar.

A team of researchers at the Ben-Gurion University of the Negev in Israel has found that the vibration patterns in a light bulb can enable us to recover full conversations from hundreds of feet away.


Light bulb: Diaphragm and transducer

But how can that be possible? The thing about the hanging bulb is that it acts both as a diaphragm and transducer. Apparently, these two, sound waves cascading on its surface and it converting air pressure from sound to small changes in light, means it is a useful gadget for intruders.

The paper states, "We show how fluctuations in the air pressure on the surface of the hanging bulb (in response to sound), which cause the bulb to vibrate very slightly (a millidegree vibration), can be exploited by eavesdroppers to recover speech and singing, passively, externally, and in real time."

Lamphone, possible with less than $1,000

The so-called "lamphone" technique can be pulled off by having a laptop, telescope, microphone, and remote electro-optical sensor for under $1,000 says the researchers.

Hackers Use Light Bulb to Eavesdrop on Conversations
Experimental setup, Source: Lamphone

The team tested the method by setting up shop on a pedestrian bridge about 80 feet (25 meters) away from a third-floor office inside a commercial building.

Hackers Use Light Bulb to Eavesdrop on Conversations
Source: Lamphone

By using a simple 12-Watt LED light bulb, they were able to accurately monitor both one sentence and two songs played via speakers in the office.

Hackers Use Light Bulb to Eavesdrop on Conversations
The recovered sentence, Source: Lamphone

Also, they state that the range could be amplified with the right gear, enabling the eavesdropper to eavesdrop for longer miles. 

Hackers Use Light Bulb to Eavesdrop on Conversations
The screenshot shows Shazam’s identification of the recovered songs, Source: Lamphone

There are some exceptions

Thankfully, there are some exceptions to this. The paper states that the hacker would need a clean line of sight between their electro-optical sensor-equipped telescope and the hanging light bulb. This means that the technique would be rendered useless if there were curtains or lampshades.

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Also, the light bulb's thickness of glass and output of light and how close the people are to it are determining factors too.

The same researchers behind the Tesla Autopilot hack

This smart and sort-of scary hack comes from the masterminds behind the Tesla Autopilot hack that tricked it into breaking the speed limit. It is a good thing that this team is working for the good of humanity since this means that a potential intruder can spy on your private conversations without needing a compromised device with malware.

While there've been instances of Alexa, Google Home, and Siri being potentially compromised using laser pointed at the device microphones, this latest research goes way beyond that since, sometimes, it looks like an intruder won't even need a "smart" device in the first place. 

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