I have been seeing a lot of tech that turn a smartphone into a wallet, usually by making a pocket for the credit cards and money. I think the next logical step would be to create something to replace another pocket weight, the keys.
This particular CalypsoKey, made by CalypsoCrystal, is an iPhone case that uses RFID chips that unlock a door within a few inches from the lock. There is less chance of hacking that way, but hopefully no one will steal your phone and try and break into your house.
Of course, that is good for one door, but what about several doors? As it so happens, several codes can be added to a single case, so that one guy with a thick key ring can abandon it. That takes a load off the belt.
Unfortunately, the user has to by the door hardware, but the CalypsoKey sells for about $100-120.