Have you ever wondered how a burglar alarm works? Its science revolves around complete and incomplete electric circuits. In this activity students will make a burglar alarm that they can use to protect something precious to them.
In this burglar alarm, a piece of cardboard prevents completion of the circuit by preventing the foil-lined tips of the clothespin from touching. Thus, when the alarm is set, the light is off. If someone steals the protected item, the thread and the attached cardboard are pulled away. This permits the foil-lined tips of the clothespin to touch, completing the circuit and allowing the electrons to flow. The light turns on, to warn you that the item was stolen.
A real burglar alarm is triggered when the intruder breaks a light or laser beam, which is invisible to the human eye, but needed to complete a circuit. When the beam is broken, the electronic system detects the change in the circuit, and sounds the alarm.