Singapore aircrew are required to wear an electronic wrist tag during layovers, similar to the ankle bracelet worn by people on bail. It's called the "Crew Safe" system. I wouldn't be surprised if the Hong Kong authorities introduce something similar. If you leave your room for 5 minutes to fill up the ice bucket it will flag up.
A contract with an airline for crew accommodation is a valuable source of income to a hotel, particularly at the moment, so a request for access to CCTV footage of the hallways around the rooms where crew have stayed would likely be granted. European data protection laws would come into this but probably wouldn't help much if matters were decided in Hong Kong.