Smartwatches are neat, but they're expensive considering what you get. Instructables user GodsTale decided the market options weren't good enough and made their own powered by an Arduino.
This smartwatch runs on an Arduino Pro Mini, a Bluetooth module, and a small OLED display. It's assembled together and then all the software's dumped onto the watch to connect it to an Android app. The end result is a watch that connects to your phone and can keep an eye on notifications, RSS feeds, and more. It could certainly use a nicer strap, but other than that it's a pretty good-looking little machine. You can see the watch in action and find a full guide over on Instructables.
Make your own smart watch [Instructables]