A remote device includes an image sensor, a readout circuit and a processing unit. The image sensor successively captures a first image and a second image containing at least one reference beacon image. The readout circuit is configured to read first image data of the first image and second image data of the second image from the image sensor. The processing unit is configured to calculate an image feature of the at least one reference beacon image according to the first image data and control the readout circuit to only read the second image data of a range of interest in the second image according to the image feature. There is further provided a power saving method of an interactive system.