Alasdair Allan & Don Coleman 
Make: Bluetooth [PDF ebook] 
Bluetooth LE Projects with Arduino, Raspberry Pi, and Smartphones

This book is where your adventures with Bluetooth LE begin. You’ll start your journey by getting familiar with your hardware options: Arduino, BLE modules, computers (including Raspberry Pi!), and mobile phones. From there, you’ll write code and wire circuits to connect off-the-shelf sensors, and even go all the way to writing your own Bluetooth Services. Along the way you’ll look at lightbulbs, locks, and Apple’s i Beacon technology, as well as get an understanding of Bluetooth security–both how to beat other people’s security, and how to make your hardware secure.