There are plenty of smart wearables you can buy these days. Some of us prefer building our own. MetaWear Coin is a low-power, Bluetooth sensor platform that lets you build your own smart wearables faster. It has an iOS/Android SDK, allowing you to develop custom solutions to communicate with the board.
MetaWear Coin has an ARM core, a motion sensor, a temperature sensor, and Bluetooth support. It lets you add your own sensors. There is also a tough, water resistant case available for the device. The project is getting funded on Kickstarter.