Speakers Doubled as Sonars to Track Your Movements at Home, say Researchers

Smart devices packing a microphones and speakers have been turned into spying tools that track your activities around the house by using acoustic pulses reflected off your body, according to researchers at the University of Washington.

Off-the-shelf speakers can be used to broadcast pulses in the 18-20 kHz range and calculate the position of people across the room by how the sound reflects off them. While the frequency can be heard by the human ear, it can be masked by music playing on the speakers.

“Our implementation, CovertBand, monitors minute changes to these reflections to track multiple people concurrently and to recognize different types of motion, leaking information about where people are in addition to what they may be doing,” reads the paper “CovertBand: Activity Information Leakage using Music.”

Researchers dubbed the attack CovertBand and claimed they have tested the proof-of-concept in five homes in the Seattle area, succeeding in tracking multiple people, even through barriers. The experiment also revealed that the 33 subjects were unlikely to detect the ConverBand attack even under ideal conditions.

“These tests show CovertBand can track walking subjects with a mean tracking error of 18 cm and subjects moving at a fixed position with an accuracy of 8 cm at up to 6 m in line-of-sight and 3 m through barriers,” according to the paper. “We test a variety of rhythmic motions such as pumping arms, jumping, and supine pelvic tilts in through-wall scenarios and show that they produce discernibly different spectrograms from walking in the acoustic reflections.”

The research proposes a couple of solutions for countering a CovertBand attack. Besides sound-proofing, and frequency-jamming, researchers also proposed the use of a Raspberry Pi with a microphone that listens for transmissions at these frequencies and automatically responds with a jamming signal. Of course, a smartphone app with the same capabilities could also be built, as a smartphone already has a microphone and speaker.

For more information on smart speakers and how they could affect your privacy, check out our videos here and here.