In almost any Dollar store you can find an inexpensive birthday card that plays the “Happy Birthday” tune (or some other) when you open it.
If you remove the works and remove the battery, you can hook up a solar panel as shown. The panel shown is 1.5 volts. (If using 1 volt panels, you would need two in series to provide enough voltage to make the speaker work.)
After removing the battery, use one alligator clip to clip together the contacts where the small piece of card slipped in and out as a “switch”, and attach the other clip to one of the two solder connections leading to the speaker. With very little light it will start playing the “Happy Birthday” tune.
Now, here’s the neat part – if you rapidly move your hand back and forth between the solar panel and the incoming sunlight, alternately shading and unshading the solar panel, the music will change pitch.
It can create a somewhat ghostly wavering sound, not unlike the Theremin, of early last century.
What is a Theremin? “The theremin is rare among musical instruments in that it is played without physical contact.”