A Pebble app that can wake your Android phone up and start it ringing so you can find it.
The Android app's repository can be found here:
https://github.com/Wavesonics/RingMyPhoneAndroid
You can install the Android app here:
https://play.google.com/store/apps/details?id=com.darkrockstudios.apps.ringmyphone
(The Android app contains the Pebble app)