One bit of functionality that I've wanted with my Pebble has been to lock my phone with a pin or password when the Pebble disconnects, thus securing my phone when I walk away from it. While it is possible to do this with a combination of Tasker and Secure Settings I was never really happy with the solution. It wasn't reliable and it was very heavy and hackish (services always running in the background and lots of root access). One of my biggest annoyances with some Android apps are that they unnecessarily run constantly in the background. To solve these issues for users that just want a very light app that doesn't need root access, I created Pebble Locker.
Pebble Locker uses the device admin API created by Google to control the lock state and password of the device. Once Pebble Locker is made a device administrator, whenever your Pebble connects or disconnects, Pebble Locker disables or enables your lock screen with the pin/password you entered. Pebble Locker also has the option to lock the device instantly upon disconnect.
The device admin API provides a reasonable amount of functionality such as disabling lock screen widgets and the lock screen camera. If you would like to see additional functionality that is not in the app, feel free to comment. Unfortunately the way I'm using the device admin API, it does not appear possible to use a pattern lock, only a numeric pin or password.