"Imagine having a private conversation with someone. You can broadcast this inaudible signal, which translates to a white noise in the microphone, to prevetn any spy microphones from recording voices," said University of Illinois researcher Nirupam Roy.
Researchers have developed an inaudible sound made up of a combination of multiple tones that create what researchers call a "shadow," a sound which microphones can detect but humans cannot. Humans cannot hear levels higher than 20kHz and microphones do not pick up sounds higher than 24 kHz.
However, researchers at the Coordinated Science Laboratory have successfully created a sound that, when interacting with a microphone's mechanics, creates this shadow of a sound, completely inaudible to humans (40 kHz or above). The sound is at a frequency that is transmitted from ultrasonic speakers, which allows it to be recorded by microphones.
There are many important and useful applications for signal, according to the team, which won the Best Paper Award at the MobiSys 2017 conference, entitled "BackDoor: Making Microphones Hear Inaudible Sounds." Some potential applications could include the government or military officials using the signal to ensure private and confidential meetings from electronic eavesdropping, or movie theaters and concert venues to prevent unauthorized recordings of performances.
The signal can also be used to send communication between Amazon Echo or Google Home, which would take some of the traffic off of Bluetooth, which is how these Internet of Things (IoT) devices communicate. This would also be a preventative measure for any unauthorized recording of communications using voice-activated systems. "We thought, can we design an application so that when you are actually giving a message, like to an Amazon Echo, no one can record your voice to the Amazon Echo if we're playing this sound?" said Roy. He added, voice-activated systems are proliferating, so it is important to defend against attacks that may be throuhg these systems.
There are, of course, some ways in which the signal could be misused, such as with hearing aids or in the case of a bank robbery, the sound could jam all of the phones trying to make calls, said Roy. But "with this knowledge of how it can be used negatively, we can develop stratgies to prevent it," said Roy Choudhury, another researcher on the team.
