Here’s something I didn’t know about hotels. Halfway through my stay at the Sheraton Wall Centre here in Vancouver, I decided to extend my stay by one night. Today I went up to my room, but couldn’t get in (the little lock light flashed red, not green).
This happens all the time to me–I think I have a wonky magnetic field that kills access cards. When I went downstairs to get a replacement, however, I learned that it was because I hadn’t received a new card when I extended my stay.
I asked, and I gather that the card knows how long it’s valid for. That makes complete sense, but I’d never actually thought through it.
I know that’s fairly lame, but what can I tell you? It’s been a busy week.
DarrenBarefoot.com 
Wouldn’t it make more sense for the _door_ (or the hotel lock computer system, in effect) to know how long the keycard is good for? Then, when you extend your stay, the card would still work without having to get a new one.
I think some hotels work that way, although I can’t recall for sure.
Nice! That way the previous “tenant” can’t get into your room after you’ve checked in even though he/she kept the card after checking out.