Well my door is going to be locked. If anyone wants to communicate he can use the interphone.
Sky marshals - tigers - call them what you like are used by some airlines - on some flights. This evil act has shown that any flight by any airline is at risk.
And all the fancy ideas about what to do with pressurisation etc. shouldn't be on the internet - available to any terrorist. In Swissair, once a hijacker was overcome by a sky marshall wielding a small champagne bottle. This news was in the paper the next day.
This is war gentlemen and the intelligence gained should be kept in company secure channels. Typically the publicity about people who were suspected for having one way tickets - the people who got demasked through simulator records mean one less chance of detection next time, as these diabolical fanatics think up new ways.