I've also been given a key card for an occupied room and entered where someone was sleeping. The reality is that no matter how upscale, the illusion of privacy and security that is presented is never going to be quite what you'd like it to be. Many people have access to the room and with electronic key cards its very easy for duplicate cards to be issued. Whenever I'm in a room I always double lock the door (with most of the rooms this is turning the knob to the far right, which prohibits entry using an electronic keycard, although can be overridden by a hard key which would probably only be available to the GM).

I spent several years working as a Navigation/Safety Officer on large international cruise ships, all officers had Electronic Master Keys however other then for the housekeeping staff we had a policy of two crew members in attendance when entering a passenger cabin for whatever reason, which for me was generally when performing safety audits or investigations of a safety or security related nature. This was really for our own legal protection and of course all entries into a room can be downloaded from the door reader to identify unauthorised access.