Wrap the end of a first 8-inch copper wire around a penny.
Wrap the end of a second 8-inch copper wire around a paper clip.
Wrap the end of a third 8-inch copper wire around a penny, then wrap the other end of the wire around a paper clip.
Mash two lemons in your hands to loosen the juice inside.
Cut two small holes into each lemon, placing the holes about an inch apart.
Place the penny end of the third wire into one of the holes of one of the lemons, and the paper clip end of the wire into one of the holes in the other lemon.
Insert the penny connected to the first wire into the second hole of one of the lemons, letting the wire hang loosely.
Insert the paper clip connected to the second wire into the second hole of the other lemon, letting the wire hang loosely.
Connect the loose wire ends to the wires of a digital clock. The juice of the lemons will complete the circuit, and will power the clock.