The PA speaker can be added to the RX1000A, RX2000A, and the AV-200 when more volume is needed than that which is provided by the RX or AV-200 alone. It is attached to the terminal screws located on the back of the RX units, or the side of the AV-200 with wire, which is included with the PA speaker. The PA speaker does not have a separate volume knob, but the volume can be controlled by the volume knob on the RX/AV-200. This PA speaker is best used in businesses that may have louder, ambient noise, like a warehouse or loading dock, and the RX or speaker alone is not loud enough to be heard. The PA speaker is an accessory only, and does not include a motion sensor or receiver.