China is actively checking people's phones at airports and land/sea entrance points for evidence that the person attended or supports the protests in Hong Kong.

China is actively checking people's phones at airports and land/sea entrance points for evidence that the person attended or supports the protests in Hong Kong. People have certainly been denied entry and held for a few hours, and may have been taken into longer-term detention. The fact that the US has been doing similar for a long time has been widely used as justification for China's actions...