"The Dark Knight" (Batman, 2009) is the one with the phone-based - is it wifi backscatter imaging - and the societal concerns.

FWIU there are contractor-grade imaging capabilities and there are military-grade see through walls and earth capabilities that law enforcement also have but there challenges with due process.

At the right time of day, with the right ambient temperature, it's possible to see the studs in the walls with consumer IR but only at a distance.

Also, FWIU it's possible to find plastic in the ground - i.e. banned mines - with thermal imaging at certain times of day.

Could there be a transceiver on a post in the truck at the road, with other flying drones to measure backscatter and/or transceiver emissions?

Hopefully NASA or another solvent company builds a product out of their FINDER research (from JPL).

How many of such heartbeat detection devices were ever manufactured? Did they ever add a better directional mic; like one that can read heartbeats from hundreds of meters awat? Is it mountable on a motorized tripod?

It sounds like there is a signal separation challenge that applied onboard AI could help with.