An indicating lamp is provided on the exterior of a vent port to indicate failure of a heater within the vent port. A first terminal connects to a first potential point between the first and second switching units, a second terminal connects to a second potential point between the third and fourth switching units. A shaft centered on the axis carries the first, second, and third fans. The notice may include an offer to establish a telephone call with the user in exchange for payment of a definite fee. The second transducer processor receives the second electrical signal from the second acoustical transducer to generate second transducer data.