Yeliz and I happened to come up with the same idea, and we figured it was challenging enough for us to work on it together.
The clock we designed is a digital sundial — it works by getting your current latitude and longitude and calculating the plot points for an accurate sundial specific to your location. The sundial updates twice daily to adjust for your current location. With this site-specific sun dial the clock can also understand your orientation relative to north. That means that you can actually know your orientation relative to the sun, and you have to align your watch to the appropriate sun dial position in order to get the shadow to point to the correct time, just like a real sun dial. If the clock is not oriented properly, the sun orientation will still cast a shadow.
This clock proved very challenging and fun to work on. Current functionalities completed are the sun dial calculator and its appropriate clock face setup. The north is also implemented on to the face so that the user can know exactly what to orient the clock to. What is left to be done is the dynamic shadow responding to the sun.
Code here: https://github.com/izkara/Sundial