Science Experiment: Build Your Own Rain Alarm

Many electrical devices are used as early warning systems such as burglar alarms, electric fencing systems and many more. Don’t you think it will be useful to have an early warning system for rain to warn you to close the windows and bring in the clothes from the clothesline? In the following science experiment you will build a device that can detect rain as soon as the first drops start to fall:


· 9 Volt battery

· Plastic coated copper wire

· 9 Volt buzzer or bell

· Clothespin

· Effervescent tables

· Wire cutters

· Rubber cement


1. Cut two pieces of thin plastic coated wire of about 2m – 3m each (or long enough to reach from the outside of your window to the inside of your bedroom where the buzzer and battery will be positioned). Use wire cutters to strip clean the ends of both wires. Make sure that one end of each wire has at least 30mm clean stripped, and the other side of each wire about 100mm clean stripped.

2. Push the 100mm stripped clean ends of both wires through a small opening in your bedroom window, and connects the other ends to the terminals of a 9-V battery, and an electrical buzzer or a bell. Use another shorter piece of wire to connect the battery and the bell to each other as in the diagram above.

3. On the outside of your window, connect a wooden or plastic clothespin to the other ends of the wires by winding it several times over each of the front ends of the clothespin. This will be your two contact pieces to complete the electrical circuit.

4. Place a small effervescent-type of tablet in between the two prongs with the contact pieces of the clothespin to prevent them from touching. You may need to experiment with several types of tables to find the most suitable one, which degenerate the fastest when coming in contact with water or ‘rain’.

5. Place the clothespin and tablet configuration on the sill of your window (you can use rubber cement to hold it in position).

6. When it starts to rain, the buzzer will go off and warn you that your clothes or curtains might get wet!

The power or ‘electrical energy’ stored in a battery can only be released and allowed to flow when a complete circuit is made out of wires or other ‘conductors’ that conduct electricity. In the above experiment, the electrical circuit is not complete until the prongs of the clothes pins with the wires wrapped around it are pressed together. When the rain drops degenerate and melt the effervescent tablet, the prongs with the wire contact pieces are pressed together, making a circular path between the battery and the bell. The current flows in a complete ‘loop’ from the battery through the ‘rain detector’ on the window sill to the buzzer and battery in your room. When the circuit is complete and the current is flowing, the buzzer sounds to warn you of the rain that started to fall!

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