Microsoft Research has been doing some research into speaker and microphone arrays as often found in smart speakers.
They have found that an array of speakers could be used for beamforming, allowing them to direct sound to a specific location in a room. This allowed the researchers to use distant speakers to create virtual headphones for example.
Even more interesting, if the speakers were ultrasound capable, the researchers could use this beam-forming capability to scan a room, and use the echoes to create images of a room.
Similar to how bats and dolphins use echolocation, we are researching the use of beamforming in the ultrasound band to construct images of objects. We can focus the sound by using a loudspeaker array facing a given direction, listen with the microphone array towards the same direction, and capture the reflections from objects in this direction. By scanning the space, we can construct an image of the objects in front of this ultrasound sensing device. The short wavelength of ultrasound allows detection of even small objects. This low-energy-using ultrasound probing device can generate three types of images: reflection, distance, and Doppler, making it possible to use in body position retrieval or gesture recognition applications.
Microsoft does not plan to use the technology for anything nefarious, but it is easy to imagine smart speaker companies using this to detect how many people are in a room, and with more sophisticated analysis what they are doing.
Read more at Microsoft Research here.