Aircraft having a alarm system like a shop set by crew on leaving, can only be reset from flight deck which is locked, so access not prevented but is known.
Perhaps an extra ad hoc cabin crew member who does not leave until cleaning, refuelling, cleaning, baggage unloading is complete is complete, same person would have to be there prior to main crew to give access to catering and refuelling (if not done earlier), sort of like a junior crewchief.
Non of that prevents a baggage handler simply leaving their smart phone in the hold as they finish up their job.