A control method of an appliance, including: the appliance includes a first unit that includes a first lamp, a first cavity, a first door and a first sensor; a second unit that includes a second lamp, a second cavity, a second door and a second sensor; and a controller that controls operations of the first unit and the second unit, includes sensing vibrations generated in any one of the first unit or the second unit by the first sensor and the second sensor; determining whether the sensed vibrations are caused by a knock, and when determining that the sensed vibrations are caused by a knock using the first sensor and the second sensor, transferring a knock-on signal to the controller; and comparing the knock-on signals received from the first sensor and the second sensor and determining which of the first unit or the second unit is given the knock by the controller, and outputting a lamp-on output signal to the first unit or the second unit in which the knock is generated by the controller.