Fun Science Projects - Make a Burglar Alarm

Fun science projects are those that teach you something about science and at the same time allow you to make something useful and fun. 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?

So how are you going to pull this off without some specialized equipment.

Easy...

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!

First up - what you are going to need:
  • 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
And here is how it is done -
  • Strip about 1cm of the plastic insulation off the one end of both wires of the flexi-wire using the sharp knife.
  • 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.
  • To the other end attach the buzzer in much the same way as you did the battery holder. To check if all is good up till now, if you attach the battery the buzzer should sound.
  • About half way down the wire cut one of the wires in half, leaving the other one in tact. Strip the ends so that about a centimeter of wire is exposed.
  • 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 end of the wire you have just stripped 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.
  • Alternatively, put a piece of cardboard or paper between the thumb-tacks that has a string attached. The other end of this string can be attached to anything that is going to move, with the idea that if that object is moved the cardboard is pulled from between the thumb-tacks.
  • Once the thumb-tacks touch - if all is in working order, the buzzer will alarm you to something out of the ordinary.
And hey presto - a simple, but very effective burglar alarm.

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