SFE has this device for sale. RF based sensor. It seems pretty powerful but wildly expensive. The "starter kit is $150 and the development kit is $600. Whew!

SFE has a Getting started with Walabot page and it looks pretty interesting. Detecting the guy's exhale is pretty amazing but perhaps the most compelling demo is where they use it to detect things in walls like the wires - the starter kit doesn't seem to have that capability. I could see a product that remodelers, housing inspectors and so on use. RF sensing seems pretty powerful. Does it have to be so expensive?

 

The retail versions are less. I see a base version on sale here for $80 https://walabot.com/diy
There is a tear down of one on AAC here https://www.allaboutcircuits.com/news/teardown-tuesday-walabot-diy-in-wall-imager-by-vayyar/