Google knowing every time I’m in the bathroom and keeping a detailed log of the times is a far cry from someone in my family happening to notice I go in there once.
I have no opinion on your reply, I was discussing technical feasibility in response to someone claiming it was infeasible. The normative claims aren't germane or particularly interesting to me.
By not exposing anyone I meant reconstructing an image. Identification is a different story and there are multiple ways on how to achieve that (heartbeat classification is an obvious one).
If you have ideas how to reconstruct an image with 4 receivers / 2-3 transmitters, please, buy a dev kit from TI (they cost <$200, https://www.mouser.com/c/?q=mmwave) and show us a demo.
I have a lot of experience with TI's IWR6843AOP chip and dev kit. It has 3 transmitters and 4 receivers and it'd be impossible to create a facial reconstruction with it.
I've just used it for the point cloud data which can be streamed via USB. If you want to stream the raw data I think you'll need https://www.ti.com/tool/DCA1000EVM. it has a 1Gbps ethernet port on it.
Gait analysis is excellent at identifying people, and that's projecting from a 2D image at a distance.
Anything which can draw a moving voxel cloud around a human is going to figure out who that human is eventually.