An electronic apparatus comprising an environment sensing device, a display, a touch sensing device, and a processing module comprising a main controller and a sub-controller is disclosed. The main controller performs a predetermined function based a touch input. The sub-controller computes a tilt angle of the electronic apparatus, and activates the touch sensing device without turning on the display if the tilt angle falls in a predetermined angle range, while the main controller is in the sleep mode. The processing module performs following steps when the display is off: determining the touch input is valid or invalid; keeping the display off if the touch input is invalid. The sub-controller wakes and activates the main controller to turn on the display and to control the electronic apparatus to perform the predetermined function according to a gesture formed by the touch input if the touch input is valid.