I remember seeing some YouTube video that politically sensitive people are under "house arrest" in a high-rise apartment, and there are plain clothes police who

I remember seeing some YouTube video that politically sensitive people are under "house arrest" in a high-rise apartment, and there are plain clothes police who guard the entrance (the apartment buildings have another gate at the beginning of the neighborhood, like a US gated community) and probably check the ID of unknown faces, ask them who they're there to see, and can refuse entry. If you said "I'm just here to see Joe Sixpack" they'll probably ask Joe if he knew you... Also, getting even a tourist/any kind of visa if your occupation is "journalist" is hard enough, I think they'd probably google you and see what you've written about China...