I guarantee you that the technology exists and they will never willingly tell us about it. Several years ago, a few private overseas firms came out with backscatter vans that can see through vehicles and homes. They can even detect what materials objects are made from. The government's secret toys are 10-20 years ahead.
They are probably very close or already able to see in 3D through walls. A drone could circle a building, send back raw radar data and have it converted to a 3D image by a powerful datacenter. 24/7, 3D surveillance is not too far off.
The days of civilization or privacy are numbered. Enjoy it will you can, FRiend...
Obviously it's possible to see just about everything on the surface inside or outside of a building, or even a deep cave or mine.
“They are probably very close or already able to see in 3D through walls. “
Done. Single system using simple delay logic. What bounces off of clothing doesn’t bounce 100% of the signal back so when it penetrates a human body it strikes the other side of the clothing and comes back again, much weaker but detectable. Only metal objects require multidimensional scanning for high resolutions but even then using scatter and collect technologies a 3D image is still possible with a single scanner, just not at higher resolutions.