A swallowable in-vivo device contains a movement detection unit that includes a movement sensing unit, a frequency analyzing unit (FAU) and a time analyzing unit (TAU). The movement sensing unit senses movements of the in-vivo device relative to a non-stationary three-dimensional reference frame, and outputs a movement signal. The frequency analyzing unit may analyze the movement signal spectrally to detect a potential command-invoking movement, and the time analyzing unit may analyze the potential CIM temporally, possibly in conjunction with a series of other movement events, to determine whether the potential CIM is a genuine CIM. If the potential CIM is determined to be a genuine CIM, the in-vivo device may execute a predetermined command associated with the CIM. Otherwise, the in-vivo device may refrain from executing a CIM-related command. A PCB including the movement detection unit and a processor for processing their output is provided for the vivo sensing device.