The sound of a greeting card or toy is produced by electronics. A battery-powered circuit contains a computer memory chip that stores a digital representation of the sound passage. Opening the card throws a switch that begins the playback. The circuit converts the ones and zeroes of the digital representation into an analog signal of changing voltages. After amplification, this signal is sent to a tiny transducer to make the sound. Remarkably, such products are not expensive, which demonstrates how mass production keeps prices down, and how the design costs per item are small when the item is sold in large quantities.