Microphones are perhaps the most common electronic sensor in the world, with an estimated 320 million listening for our commands in the world’s smart speakers. The trouble, of course, is that they’re capable of hearing everything else, too. But now, a team of University of Michigan researchers has developed a system that can inform a smart home—or listen for the signal that would turn on a smart speaker—without eavesdropping on audible sound.
The key to the device, called PrivacyMic, is ultrasonic sound at frequencies above the range of human hearing. Running dishwashers, computer monitors, even finger snaps, all generate ultrasonic sounds, which have a frequency of 20 kilohertz or higher. We can’t hear them—but dogs, cats and PrivacyMic can.
The system pieces together the ultrasonic information that’s all around us to identify when its services are needed, and sense what’s going on around it. Researchers have demonstrated that it can identify household and office activities with greater than 95% accuracy.