However, I suspect SpaceX will however allow China to monitor/limit connections. Further, China has a lot more power to crack down on purely internal operations would deter many.
a) the rooftop CPE needs to be reasonably large and have high gain to be used effectively, and needs clear unobstructed line of sight to as much of the sky and horizon as possible.
and
b) It needs to transmit, it will transmit in very known frequency ranges, and the chinese authorities have plenty of budget to buy portable spectrum analyzers, horn antennas and to reach people how to use them. It only takes a couple of hours maximum to reach somebody how to use a portable spectrum analyzer to physically locate and identify transmitters in almost any band.
B) These things need to transmit up, so you can reasonably block most signals in other directions. Aircraft would work, but again not cheap.
The real issue is more on the human side and network monitoring. Lots of encrypted network traffic to a ransom location would be suspect.
PS: For once tinfoil might actually be useful vs government spying :)
B) not just up but to the sides and toward the horizon as well. This will be a non moving phased array antenna that can talk to two LEO satellites moving across the sky at the same time. I predict that any reasonable amount of blockage to the sides will not be a good idea for their network architecture.
C) all Tx have some sort of sidelobes and nothing has a perfect f/b ratio. Will still be detectable by spectrum analyzers from the side.
B) Depends on how many satellites are in the constellation. Ideally you want a lot of them as there is vastly more atmosphere the lower your angle to the horizon.
C) detectable at say 50 feet sure, but a signal you can detect from 10+ miles in a van doing 60mph without a lot of false positives is another story.
With the resources of China, spending $15,000 per spectrum analyzer kit x 8 kits, plus training, is a tiny drop in the bucket compared to the amount of money and effort they are currently spending on IP cameras that feed into facial recognition systems, etc.
However, if you want to catch individual usage in urban areas, with guys on for that's going to easily be into the 10's of of billions as users don't need to keep them on 24/7. AKA within the capability of nation states, but not without significant effort.
s/Aircraft/Drone/. Now it's cheap.