An electronic system is provided, which includes a first device and a second device. The first device includes a light source unit, a light detection unit and a control unit. The light source unit is utilized for emitting light along a light path. The light detection unit is utilized for detecting reflected light and measuring intensity of the reflected light. The control unit is utilized for generating a control signal according to the intensity of the reflected light. The second device includes a switch body and a reflection portion. The reflection portion is disposed on the switch body. When the reflection portion is located on the light path, the reflection portion reflects at least a portion of the light to form at least a portion of the reflected light.