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Fun science projects
Make a burglar alarm

Background

Fun science projects are those that teach you something about science and at the same time allow you to make something useful and fun that you can play with after the project has been graded. This is one of those projects!

The job of a burglar alarm is basically to tell you when someone who shouldn't be in your house has come in – not so? And where will these nasties come in? Through a door or window – right? So if we can make something that will tell us when a door or window has been opened that should not have been opened, we would know when someone, who shouldn't be coming in, is in fact coming in – right?

And what about your baby brother who keeps sneaking into your room to help himself to your stash of candy? Now something that tells you when your door is being opened would be really useful in that situation...not so?

Let's do science...

The Experiment

You are going to use simple circuit that when closed with a switch will set off an alarm. The switch is going to be a clothes peg!

The Aim

Apart from being one of those fun science projects, the aim is to make a simple burglar alarm using electronics and a clothes peg as a switch.

Equipment Needed

  • Approximately a meter of flexi-wire
  • A 9V battery (the correct scientific term is a cell)
  • A 9V battery (cell) holder
  • A wooden clothes peg
  • 2 thumb tacks
  • A sharp knife
  • Electrical insulation tape
  • An small electric buzzer

    Method

  • Strip about 1cm of the plastic insulation off the one end of both wires of the flexi-wire using the sharp knife. If you are not sure how to do this, get an adult to help you.
  • Attach both wires of the one end of the flexi-wire to the battery holder by joining the wires together and then wrapping insulation tape around the joins.
  • Cut the wire and strip it as necessary about 15cm from the battery attachment. Attach the buzzer as necessary. (It is difficult to say how to attach the buzzer as each one will be slightly different. But once everything is set up, you can play around with the connections until you find the right one. This is the best way to learn, and it is scientific as you are experimenting!!!!)
  • Press the thumb tacks onto the inside of the opening end of the clothes peg. Before you push them all the way in, place the other ends of the flexi-wire under each of the thumb tacks and push them in hard so that the wire is held there.
  • Attach the battery. If everything is attached correctly, with the clothes peg closed, the buzzer should buzz. If it does not, you need to check your connections on the battery, buzzer and peg.
  • Once everything is working, open the clothes peg and jam it into the gap of a door and it's frame or in a slightly open window.
  • Open the door or window and see what happens!

    Results

  • If everything is connected properly, when the clothes peg is closed, the buzzer should buzz.
  • Once it is opened, for example when it is jammed in the gap between the door and it's frame or in the slightly open window, it will not be making any noise.
  • As soon as the window or door is opened, the clothes peg will fall out, and close. This will close the circuit again and the buzzer will buzz. (Apart from making a burglar alarm, you can imagine the fun you could have with such a device - yup, as I said, this is one of those fun science projects!)

    The Conclusion

    By creating a circuit with a buzzer and a switch that closes the circuit when the door is opened, a simple burglar alarm can be made. (In other words - noisy buzzers with peg switches equals fun science projects.)

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