You may think RFID tags are a pretty decent way to track your property, but Microsoft is trying to patent a much higher-tech system. A Hololens-like augmented reality device would scan your surroundings and keep tabs on objects like keys, wallets or other things. Then, if misplace something, it would guide you straight to where it saw it last.
To set up tracking, you could scan specific objects by holding them up to the display so that it doesn't track flowerpots, books and everything else in the room. A mobile device or headset like Microsoft's Hololens (above) could then store its last location, position, state or other characteristics. In one example (below), if the system notices that your keys were covered by a newspaper, it'll "highlight [them] on the see-through display" when you ask where they are.
In other cases, the device "may adaptively learn which objects to track" by determining their importance, presumably by some kind of AI scheme. It could also do things like remember how much milk you have and remind you to get some when you're at the store. So in sum, Microsoft is throwing motion tracking, object recognition, and possibly artificial intelligence at the problem of ... lost keys.
While I do mislay objects and enjoy augmented reality, I feel that Microsoft is throwing wayyy too much tech at this. There are plenty of other lost object solutions that work just fine, like RFID tags or Bluetooth trackers, for one thing. Mainly, I'd like to see Microsoft's engineers spend time on more important Hololens features, so that I can start playing IRL first-person shooter games in the office like I was promised.