One of the most irritating things people have to deal with today is losing keys. Losing keys often means frantically running around town trying to remember what you did the night before, and often means hundreds of dollars in Locksmith fees.
My app is built for anyone who loses their keys, or generally in the habit of losing keys or other valuables.
The feature I am most proud of is the detection of the keys in the pocket. I use the built in magnetometer in many phones that is used for compass orientation to find the metal in my pocket, in this case my key. When it no longer detects that metal, it takes a gps coordinate telling me where I lost my key.