The present contribution is motivated by recent studies on the assessment of the fluency of body movements during complex motor tasks. In particular, we focus on the estimation of the Cartesian kinematic jerk (namely, the derivative of the acceleration) of the hips' orientation during a full three-dimensional movement. The kinematic jerk index is estimated on the basis of gyroscopic signals acquired through a smartphone. A specific free mobile application available for the Android mobile operating system, HyperIMU, is used to acquire the gyroscopic signals and to transmit them to a personal computer via a User Datagram Protocol (UDP) through a wireless network. The personal computer elaborates the acquired data through a MATLAB script, either in real time or offline, and returns the kinematic jerk index associated to a motor task.