Make Your Own Burglar Alarm

Recommended Age Groups: Later Elementary, Middle School
About this lesson from Peter Cabauy

Introduction

So you want to make a burglar alarm.
The question is, why?

When I was in Elementary School, I had my lunch stolen from me almost every day. It would really get me angry at lunch time, because I knew it was Paul, but I couldn’t prove it.... (Continuation)

Let’s begin!

Materials

1. Insulated Wire
   • Get 4 strands of wire, each 1 foot in length
   • You can find the wires around the house, inside battery-operated appliances that no longer work. Make sure that your parents give you permission to take them apart.
   • You can also buy the wires and other supplies listed from a Radio Shack, a hardware store, or the electrical section of big stores like Walmart.
   • Note: In order to make this alarm, you will need to peel off the rubber/plastic insulation from two of the wires. Try to peel the wires before starting this lesson. If it is too difficult for you, then you can buy non-insulated wire that does not need peeling.
2. 1.5-volt battery.
3. Kite string or button-and-carpet thread, 3-5 feet long.
4. Scissors
5. Electrical tape
6. 1.5-volt mini-buzzer
7. Spring-type wooden clothes pin
8. A scrap piece of board or plywood 4 inches by 12 inches or bigger.
9. Super Glue

Principles

The best way I know to build something is to understand every individual part. The burglar alarm is made of three parts:

1. The device that makes noise - a buzzer
2. The battery
3. The buzzer switch

The Buzzer

We cannot have an alarm without something that makes sounds. That is why we use a buzzer, which is something that makes a loud sound. To make the sound, the buzzer needs to be connected to the battery.

The Battery

The battery is very important to the alarm. For the buzzer to work, it needs energy. This energy comes from the battery. If the buzzer is not connected to the battery, it will not work. You have a switch to control this connection.

The Buzzer Switch

See how the buzzer works by connecting your 1.5-volt battery to the buzzer directly. (The buzzer should come with two different wires. If the wire is insulated, you will need to peel a small length so that you are able to see the metal wire inside.) Get two other pieces of wire and connect them to opposite ends of the battery. Connect one wire to (+) and the other to (-) (see diagram 1). In diagram 1, the battery should have the (+) and (-) labeled. Also, if you look closely, there is a (+) and (-) on the battery that you bought.

You may want to use electrical tape to hold the wires in place on the battery.

Connect the buzzer’s wires and the battery’s wires by twisting them, just like in the diagram 1. The buzzer should be making a sound; if it does not, check the connections at the ends of the wires to the battery.

Question:

• What happens when you disconnect a wire from the buzzer?
  Now, connect it again as often as you want and see how the buzzer turns on and off. By connecting and disconnecting the wires, what you have made is called a switch.

When you disconnect a wire and the buzzer stops sounding, we say that the switch is open. When it is open, no energy from the battery reaches the buzzer.

When you connect the wire and the buzzer sounds, we say that the switch is closed. When it is closed, the energy from the battery reaches the buzzer.

Making the Alarm

1. Disconnect one battery wire from the buzzer.
   
   
2. To make things easier, put the battery and the buzzer on the wood, as shown in diagram 2.
   
   
3. Use a piece of electrical tape to tape the battery to the wood so that it does not move.
   
   
4. Get the buzzer and put it at the other corner of the wood and tape it to down, just as in diagram 2.

Now that you have taped the battery and the buzzer to the wood, we will work on the most important part of the burglar alarm, the switch. The burglar alarm switch is a little different from the buzzer switch that you made by disconnecting and connecting the wire at the beginning of this lesson.

Now you want a switch that works easily and more quickly, without you having to make and break the connection with your hands. You need a switch that turns on and off the buzzer depending on a door opening or closing. Making a switch that does this will result in a Burglar Alarm Switch.

The Burglar Alarm Switch

1. First, you will need to wrap the ends of the clothes pin with the non-insulated wire or the insulated wire that you have peeled. Look at diagram 3.
   
   

   

2. Make sure that the wires touch when the clothes pin closes, as in diagram 4. If the wires don’t touch, then there will be no connection and the alarm will not work.
   
   
3. After wrapping the wires, connect one of the free ends of the wire to one of the wires coming from the battery.
   
   
4. Connect the other wire from the pin to the buzzer.
   
   

   

5. Connect the remaining free wire from the battery to the buzzer (if you have not yet done so when making the buzzer switch, above).
   • Note: If you are confused by now, just look at diagram 5 and connect the wires as shown in the picture.
   
   
   
6. Test the switch by opening and closing the pin. When the clothes pin is closed, the alarm should sound. If it doesn’t, make sure all the wires are connected and that the clothes pin’s non-insulated wires on the end are touching. If it still does not work, look at diagram 5 and check all the wires again. It should work.
   
   

   

7. When it is working, you may want to turn it off by placing a small piece of cardboard in between the ends of the pin so as to open the switch and turn off the buzzer. It is annoying to continue working with the buzzer on. (See diagram 6.)
   
   
8. With the buzzer off, paste the clothes pin to a corner of the wood using crazy glue (see diagram 7).
   
   CAUTION:
   You have to be careful with the glue. It sticks very quickly. Do not touch the glue with your fingers. It might be a good idea to have some nail polish remover handy: if you accidentally get your fingers stuck together, it can dissolve the glue for you.
   
   
9. Finally, attach the string to the cardboard that you already put between the ends of the pin. When this string is pulled away, the wires in the pin will make contact and the alarm will sound.
10. You are done!

Now you have a burglar alarm. Just tie the string to a door tightly, so that when the door is opened, the cardboard is pulled out and the alarm sounds.

Have fun catching people who walk into your room or just someone who is stealing your lunch box!

Careers Related to Lesson Topic

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Prerequisite Vocabulary

insulated:

when a wire is insulated, it is has a plastic or rubber cover. This cover does not let electricity pass from the sides of the wire. The rubber or plastic cover is usually in different colors, but inside, the wire itself is golden.

non-insulated:

this means the opposite of insulated. This wire is not covered and, for this reason, electricity passes through the sides. A non-insulated wire does not have any colorful covers, so it has a golden type of color (the color of the wire).

volt:

the unit in which electricity is measured. Example: you might have a height of five feet. Your height is measured in feet. A battery has an energy of nine volts. The battery’s energy is measured in volts.