A remote controller for controlling a display device includes a first image sensor, a processing unit and an activation mechanism. The first image sensor is for sensing an object and forming a digital image. The processing unit is coupled to the first image sensor for calculating image variations of the object on the digital image, correspondingly controlling the display device according to the image variations and deactivating the first image sensor after the remote controller is idle for a predetermined period of time. The activation mechanism is coupled to the first image sensor for re-activating the deactivated first image sensor.