I looked up prepared piano on wikipedia, and the article gave a number of early examples of ways piano makers added sounds to the piano. Here was my favorite:
Turkish stopAround the turn of the nineteenth century, Turkish music was so popular that piano manufacturers made special pianos with a Turkish stop, also called the military or Janissary stop. The player would press a pedal that caused a bell to ring and/or a padded hammer to strike the soundboard in imitation of a bass drum. The Turkish stop was popular for playing the famous Mozart Rondo alla Turca, K 331.