Fitbit Flex

Flex by Fitbit is a flexible wrist band which includes a sensor to record activities and sleep. The data collected is similar to the Fitbit One:
 * Steps taken
 * Distance covered
 * Calories burned
 * Active minutes
 * Sleep (hours slept, times awoken, sleep efficiency)

The flex can wake you up with a silent vibration alarm. The device is water-repellent (but don't swim with it) and the sensor can be removed (and used with other flex wrist bands). Contrary to the One the Flex can't be used to count stairs climbed. It is synchronized via USB and can be used via the Fitbit app.