create music by ringing up items

To get the word out about the Prague Spring Classic Festival, they created a promo at a shop that allowed customers to create their own sheet of music on the checkout line. To do so, they drew a musical staff on the cash register tape, which had indicators that detect the location of items scanned. So when the cashier is ringing up the sale, piano sounds come from the speakers. End result? Your receipt is printed showing you the musical composition you created.