TI (Texas Instruments) SensorTag (http://www.ti.com/tool/cc2541dk-sensor) is a nice dev board that suits well to prototype this project.

SensorTag is packed with a lot of MEMS sensors, including a Kionix KXTJ9 Tri-Axis, User Selectable ± 2g, 4g, 8g, Digital (I2C) Output, 3x3x0.9mm LGA Accelerometer (http://www.kionix.com/accelerometers/kxtj9) and an InvenSense IMU-3000 Triple Axis MotionProcessor™ Gyroscope (http://www.invensense.com/mems/gyro/imu3000.html).

SensorTag is powered by a CR2032 battery cell coin and is BLE (Bluetooth 4.0 Low Energy) enabled.

It is small enough to attach it to any shoe or to simply put it in your socks. The blue thing from the pictures is the size of a credit card.

This is the beast:

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