Note that a conspicuous capability of a Predator drone is to track people's heat signatures, with limited capability into buildings.
Seems tech may have received some upgrades:
https://www.technologyreview.com/2019/06/27/238884/the-penta...
There was also a hot-air balloon program that would persist at stationary at high altitude and track all moving targets over a metropolitan area for up to a month without maintenance.
The news article which said the project was called "Basilisk Stare", seems to have vanished now though from all search results. Edit: Maybe I'm misremembering and its actually Gorgon Stare.
They could do this with a single (bajillion dollar) military radar slung from the bottom of a plane over Iraq 15yr ago.
The current tech is probably cheaper and better.