If you use sensors with a Raspberry Pi or Arduino in your home network, you may want to get desktop notifications on your Linux PC whenever some interesting event is detected. You can send messages via SSH or through simple TCP connections and display them with notify-send.
Use the buzzer to have your MCU play small wake-up melodies, signals, or music to accompany LED animations. The sound might not be a feast for the ears, but it does give your projects a great retro feel.