alt Hacker NewsIt's already been decided by SCOTUS that things like heat imaging require a warrant, and that arbitrary scanning without a warrant (or presumably also probable cause) is a violation of the 4th amendment. This technology (still science fiction) would likely get similar treatment using the existing precedent about how new technologies can be used.
The easy workaround for this (which Flock has used to massive success and why it's drawn so much ire) is to set up or subcontract a private corporation to do this which will inherently be subject to much less stringent oversight. It also allows government and law enforcement to evade accountability.