first and foremost it would require knowing the exact position of the person's head.
That's really not difficult with camera tracking.
And yes they are real waves that can be recorded or detected.
I'm not asserting whether it is deployed or not. Just that the technology does work.
I have been working with/around RF for a few years and try to stay up to date with the theory. I'm not sure if I'd say expert but a lot of the theories of what the effects of 5G are don't hold water. I also wasn't defending 5G, just saying something using ultrasonic waves has nothing to do with 5G
There have been working devices with this principle made https://youtu.be/yEM4yXKlHi8
I find it highly unlikely this is default on and not some instagram or snapchat filter