I've been grousing about how much I really want something like this for cars specifically for key-sharing. My driveway is four cars deep and two wide, so my va

I've been grousing about how much I really want something like this for cars specifically for key-sharing. My driveway is four cars deep and two wide, so my various housemates all have to make a copy of their key available so we can move any cars blocking us in. If we could just generate a sub-key, that'd be much more convenient. Similarly, how about the ability to easily give a temporary house key to your visiting friends/family without having to have n spare keys sitting around? (Right now we have a re-programmable keypad, but if we could generate temporary subkeys without either giving out the master code or programming in a subcode, that'd be ideal.)