The Extra Wireless Receiver for Wireless Motion Alert plugs into a standard wall outlet and can be placed on a table or mounted on the wall (mounting materials sold separately). When the receiver gets a signal from the transmitter, one of four user-specified tones (Classical, Westminster Chime, Ding Dong, or Whistle) will sound for a few seconds. There is also a volume control, allowing you to set the sound to the desired level.