Almost everyone carries at least one microphone and two cameras on their person at all times, along with a WiFi system that researchers have demonstrated can be used as a wall-penetrating radar capable of pose estimation, heart-rate sensing, and breath sensing.
Monitoring with all these things can be done at low-quality in real-time using the compute attached to those sensors, anything that might be interesting can be automatically passed on to a higher level system.
Smart dust was discussed quite widely until very recently, and as all the parts of that are now basically ready, I think the stuff has actually been made and is currently being actively (but quietly, under NDA) investigated by intelligence agencies both for potential uses and potential countermeasures.
A few years ago, I did a Fermi calculation and my conclusion was that a laser microphone pointing at every window in Greater London would cost about the same as the annual budget of the Met Police.
At 128 kbit/s (e.g. for decent compressed audio), recording all 8 billion humans on Earth for a year (24 hours a day so even while asleep) would require about 4 ZB of storage; current storage prices were around $14/TB in 2022, which would thus cost $56 billion compared to $73.4 billion the US Director of National Intelligence requested for the Fiscal Year 2025 National Intelligence Program.
We don't talk about the information explosion "problem" because there isn't actually a problem: all the data on the internet has to be processed anyway just for people to be able to see it in the first place, and for quite some time now all the data we care about is on the internet anyway.
