RIFD / WIFI locator?
I would think that an old dual antenna wireless G router could be used in combination with an RFID tag. So when the tag is moved to a new location within range of the router the location will be saved or displayed on the computer screen.
I thought that having a system like this would be great for keys, animals, phones, babies, pills, etc.
Here is one example application:
Where are my keys? - open the web browser and retrieve the approximate location where the keys were last moved. They are in between the sofa cushions.