An energy saving method for acquiring in vivo images of the gastro-intestinal tract is provided. A device, such as an autonomous capsule, includes at least one imaging unit; a control unit connected to the imaging unit and a power supply connected to the control unit. The control unit includes a switching unit and an axial motion detector connected to the switching unit. The axial motion detector detects the axial movement of the device and if the axial acceleration is below a pre-determined threshold, disconnects the power supply thereby preventing the acquisition of redundant images. A method for operation and use of the device is provided.