An electronic device includes: a sensing system having a first sensing device, for selectively detecting an object to generate a first detection result at a first frequency, wherein the first detection result indicates a state of motion of the object; a second sensing device for selectively detecting the object to generate a second detection result at a second frequency that is different from the first frequency, wherein the second detection result indicates whether the object is in a specific space; a light emitting device, for illuminating the object to make the first sensing device able to detect the state of motion of the object; and a control unit, coupled to the first sensing device and the second sensing device, for controlling operating states of the first sensing device and the second sensing device according to the first and the second detection results.