Put them and all valuables in the ship's safe deposit box. Use all locks on the door including the night latch, and don't open your cabin door to strangers. Whatever the person wants can be expressed from the other side of the closed, locked door. Don't assume that you are safe from criminal acts. While there is little danger of an outside predator robbing or attacking you on a cruise ship, crimes can just as easily be committed by crewmembers or by fellow passengers.
Many cruise lines hire transient employees at low wages.
Because of this, employee turnover generally is often high, and cruise lines struggle to keep a ship fully staffed. While most crew members are hardworking, honest people, you cannot assume that the ship has fully screened its attendants, waiters or below-deck crew. Stay only in the public areas. On modern cruise ships, security personnel are on board and patrol in plain clothes. Occasionally security will monitor video displays.