Microphones in smartphones built specifically to hear human voice. Humans can’t hear at levels higher than 20 kHz, and microphones max out at around 24 kHz.
Now, researchers at the University of Illinois have designed a sound that is completely inaudible to humans (40 kHz or above) yet is audible to any microphone. The sound combines multiple tones when interacting with the microphone’s mechanics creates a “shadow,” a sound that the microphones can detect.
“Imagine having a private conversation with someone. You can broadcast this inaudible signal, which translates to a white noise in the microphone. To prevent any spy microphones from recording voices,” said Roy, a PhD student.
According to the researchers, military and government officials could secure private and confidential meetings from electronic eavesdropping or cinemas and concerts could prevent unauthorized recording of movies and live performances.
The signal can also used to send communication between IoT devices. Which would reduce the growing load on Bluetooth, since Bluetooth is primarily how IoT devices communicate. This signal could protect users from unauthorized recording when communicating with voice-activated systems. Voice-activated systems are important to build defenses against attacks that can launched through your voice.
The sound’s frequency designed by researchers and transmitted from ultrasonic speakers, completely inaudible to humans, but recorded by microphones. The team acknowledges there may be ways to misuse this technology. Though they hope that by knowing the problems that can arise, they can build measures to protect against it.
Inaudible sound jammers could affect someone wearing a hearing aid because the internal microphone would pick up that sound, said Roy.
The sound frequency is transmitted from ultrasonic speakers, but the signal of microphone receiver is not altered in anyway. Off-the-shelf microphones will react in the same way to the signal.
Researchers said, Microphones are in millions of devices, including all of our smartphones. This signal can be received without modifying microphone, making this technique readily available to interact with the devices around us.
More information: [BackDoor]