Guang-Zhong Yang, Ph.D, and his colleagues at Imperial College in London have been developing a sensor worn behind the ear that tracks a variety of user information, and transfers it to a computer for real time analysis. They hope it may will mass-produced within 12 to 18 months. It's currently being tested in atheletes, and individuals recovering from surgery.
From MIT's Technology Review:
The sensor is about the size of a cuff link and measures the posture, stride length, step frequency, and acceleration of an individual. In addition to being used in applications for training athletes, the device could be employed to monitor a patient's recovery after surgery, such as orthopedic, or injury, such as a fracture. In those cases, an individual will often compensate for the affected area, which impinges movements, says Yang. The device could also be used to monitor an individual suffering from a progressive illness, such as a neurodegenerative disease: it could detect telltale changes in the person's movements.
The sensor uses an accelerometer that allows it to measure motion in three dimensions. For example, when a runner hits the ground, a shock wave is transmitted through his body from his foot. The accelerometer is able to pick up these waves and sense the balance of the body and the changes in the runner's gait, such as the length of strides and the frequency of steps.
This information is processed within the sensor and wirelessly transmitted to a computer...