Alarm systems are great, especially the high-tech ones that detect an intruder by the heat he or she gives off. In this experiment, you’ll get to construct an alarm device and use it to assemble a circuit.
Things Required:
Two connecting wires with each end stripped 1½ inches bare of insulation
Simple buzzer circuit
10 inch × 3 inch cardboard
Pair of scissors
2-inch strip of aluminium foil
Tape
Directions:
Cut out a strip of cardboard (removed from a packing box) that is about 10 inches long × 3 inches wide. Bend the strip in half to form two 5-inch-long sections. Wrap the middle of each section with a 2-inch strip of aluminium foil. Use tape to secure the strip. Attach two 1-foot long wires to the outer side of each strip. These wires are attached to a series circuit that contains two 1.5-volt cells and a buzzer. The folded cardboard should be placed beneath a carpet or mat. Make sure the weight of the carpet doesn’t close the halves together. Once the alarm detector is “set,” just sit back and wait.
This Is What Happens:
The alarm detector is a pressure switch. The weight of the carpet is not great enough to press fully the cardboard halves together. Therefore, the switch remains open. When someone stands on the carpet, however, their added weight closes the switch. Once closed, the current can flow from the battery to the buzzer and sound the alarm!
