Fun science projects are those that teach you something about science and at the same time allow you to do something useful and fun. This is one of those projects!
The job of a burglar alarm is basically to let you know when someone who shouldn’t be in your house has broken in, they don’t. And where will these nasties come in? Through a door or window, right? So if we can make something that tells us when a door or window has been opened that shouldn’t have been open, we’d know when someone, who shouldn’t be coming in, is actually coming in, right?
So how are you going to accomplish this without some specialized equipment?
Easy…
You are going to use a simple circuit that, when closed with a switch, will trigger an alarm. The switch is going to be a clothespin!
First, what you will need:
- Approximately one meter of flexible cable
- A 9V battery (the correct scientific term is cell)
- One 9V battery holder (cell)
- A wooden clothespin
- 2 thumbtacks
- a sharp knife
- electrical insulation tape
- A small electric bell
And this is how it’s done:
- Strip about 1 cm of the plastic insulation from one end of both wires of the pigtail with the sharp knife.
- Attach both wires from one end of the pigtail to the battery mount by joining the wires together, then wrapping electrical tape around the joints.
- At the other end, connect the buzzer the same way you connected the battery holder. To check if everything is ok so far, if you connect the battery, the buzzer should sound.
- About halfway through the wire cut a wires in half, leaving the other one intact. Strip the ends so that about a centimeter of wire is exposed.
- Press the thumbtacks into the inside from the opening end of the clothespin. Before you push them all the way in, place the end of the wire you just stripped under each of the thumbtacks and push them in hard so the wire is held there.
- Connect the battery. If everything is placed correctly, with the clothespin closed, the buzzer should sound. If not, you need to check your connections at the battery, buzzer, and pin.
- Once everything is working, open the clothespin and stick it in the gap between a door and its frame or a slightly open window.
- Alternatively, place a piece of cardboard or paper between the thumbtacks that has a string attached to it. The other end of this string can be attached to anything that is going to move, with the idea that if you move that object, you pull the cardboard out from between the tacks.
- Once the thumbtacks touch, if everything is in order, the buzzer will alert you to something out of the ordinary.
And voila: a simple but very effective burglar alarm.