Check out MetaWear, a Bluetooth and processor module aimed at app developers who want to get prototypes up and running quickly:

Instead of uploading your code to the micro-controller board, it comes pre-loaded with its own custom firmware — sort of like an Arduino running Firmata — and you talk to the board from the MetaWear’s Android and iOS SDKs, or using a generic Bluetooth LE library like noble from node.js. In other words, you don’t have to worry about cramming the smarts of your wearables into the limited computing power of the board itself. Instead, you use your smart phone and its sensors — accelerometer, magnetometer and gyroscope — and location information — Wi-Fi and cell positioning, and GPS — without having to roll out any hardware.

via MAKE