An input interface device includes a sensing panel, a touch sensor, an auxiliary sensor and a processor. The touch sensor is configured to detect a first touch event located in a first area of the sensing panel, and detect a second touch event located in a second area of the sensing panel. The first area and the second area are separated by a first boundary defined across the sensing panel. The auxiliary sensor is configured to detect a first environmental parameter. The processor is configured to determine whether the first boundary needs to be adjusted or not according to the first environmental parameter. The processor is also configured to selectively adjust the first boundary according to the first touch event and the second touch event, and the first boundary after adjustment is utilized to separate the first area and the second area.