The clothes pin and paper clips are a switch. When the paper clips touch, the circuit is complete. The current runs from the battery
- through the wire to one of the paper clips,
- from one paper clip to the second paper clip,
- from the second paper clip through the wire to the buzzer,
- from the buzzer through the wire and back to the battery.
Anything that separates the two paper clips opens the circuit. When the circuit is open the buzzer stops. In the money alarm, the paper money separates the two paper clips.
What do you think would happen if the money was a penny or dime instead of the dollar?