This document describes WearDuino, an open source wearable wireless sensor. It can be worn in various locations on the body through accessories like hats, shirts, wristbands, or socks. The core hardware consists of a small board with Bluetooth, sensors, and a battery. Optional sensor boards can add capabilities like heartbeat or flexion detection. The system is designed to be customizable so users can build exactly what they need. It aims to give users control over their own health and activity data.