This app provides examples of how to use the MetaWear API and a simple app for interacting with the board. It uses the sample BluetoothLeGatt app on the Android developer page and the Nordic nRF Toolbox app as references.
http://developer.android.com/samples/BluetoothLeGatt/index.html
https://play.google.com/store/apps/details?id=no.nordicsemi.android.nrftoolbox&hl=en
The API was built in Android Studio 1.3.1. It is targeted for Android 5.1.1 (SDK 22) with Android 4.3 (SDK 18) as the minimum required SDK, and requires a JDK compiler compliance level of 1.7.