Really cool idea, but I think any system like this needs to have a fail-safe option, for when your phone runs out of batteries.
I thought enough people knew by this time that storing all your passwords in plaintext file on desktop is insecure. Why do you even need a phone if you have a key somewhere on the property.
Nobody's going to find your emergency spare key if it's left in a non-obvious place; there are no rings of thieves with metal detectors scouring half acre properties.