[Animats]

Whatever happened to that Google millimeter radar project to allow devices to see your hand positions? It ended up in the Pixel 4 as Motion Sense, but all it does is let you make swiping gestures in the vicinity of the phone. There should be more useful applications for that technology.

[Reelin]

It's not limited to Google. For example, this TI mmWave sensor (http://www.ti.com/product/IWR6843) has an associated reference design for gesture control (http://www.ti.com/tool/TIDEP-01013).

(Disclaimer: I've never actually used that chip or reference design and have no idea how well it actually works in practice. I just think it's really neat that mmWave radar chips are readily available at very affordable price points.)

[syphilis2]

The last application I saw was using micro Doppler signal recognition to determine if someone has fallen down. Consider a nursing home or hospital bathroom where cameras would be considered intrusive.