The Williams by Bachmann True Blast Plus Sound Unit is just the thing for adding realistic sound to select Williams O Gauge locomotives. The sound unit includes a circuit board, speaker, speaker enclosure and full installation instructions for adding 16-bit polyphonic sound including prime mover, horn and bell.WARNING: This product can expose you to chemicals including Lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov