STEM activity: How to Build a Burglar Alarm

Details on how to build a simple burglar alarm from simple components including newspaper, tin foil, wire, battery & a buzzer.

STEM projects & activities includes:
How to Build a Simple Burglar Alarm

This "burglar alarm" is a simple project that can be used for STEM and provide an afternoon of fun building it, and then many more hours catching the family out.

Place the detector pad under a mat where you want to catch someone, and simply wait for them to come along and stand on the mat and they will be "caught." Great fun for all the family and for the young ones to build under supervision.

The STEM burglar alarm project can be built from a few objects that can be bought quite cheaply from Amazon, or other electronic component stockists and it can be built by relatively young, but probably with help from an adult.

I seem to remember I devised this simple burglar alar project when I was about nine or ten, and then tried it with my children and then my grandchildren. It requires a little care and attention as it uses items that are easy to obtain and many can be found from around the house.

Electronic components required

Very few electronic components are needed for the STEM burglar alarm project. Although a buzzer and battery holder as well as a battery are needed, the other items can generally be found around the house.

1 sheet newspaper or A3 sized paper - size not particularly important, but as a guide it can be around 35cm x 25 cm
2 pieces of tin foil - these should be cut so that about about 1 inch / 2.5 cms of newspaper shows when placed on the newspaper
Tape, either masking tape, sellotape
Connecting wire such as bell wire
Buzzer
Battery connector
Battery

We bought a buzzer and battery holder pack from Amazon - these buzzers operated from 3 - 24 V, and the battery holders were for 9V batteries. The Bell wire was again bought from Amazon. The total cost was around £10 / $10.

Making the burglar alarm can be split into three sections: making the pressure sensor or mat, making the buzzer section, and joining it all together.

Making the STEM burglar alarm pressure sensor

The instructions for the STEM burglar alarm can be split into several easy stages.

For this stage of the STEM burglar alarm, the two sheets of tin foil, the newspaper sheet, the bell wire and some tape are needed.

Take the sheet of newspaper and fold it in the centre.
Cut five small triangles on the fold equally spaced. They should be about 1 cm along the fold and half a centimetre deep. These are only guidelines to give the approximate size of the hole.
Undo the centre fold and fold again, but half way between centre fold and the edge.
Repeat cutting of holes along the rest of the fold.
Unfold the paper and fold the other side of the centre fold and repeat.
Repeat hole cutting again. You should end up with a piece of newspaper with 15 holes in it.
Take one sheet of tin foil and place it down onto the newspaper. Ensure that it is centrally placed and the edges do not overlap the edge of the newspaper.
Carefully tape the tin foil down onto the newspaper - either small bits in each corner, or along the edges if you think that best. Use the Sellotape, masking tape, etc.
Turn the newspaper and foil over so that the bare side is showing.
Carefully sellotape the tin foil down onto the newspaper as before.
Locate the bare copper wire over an area of the tinfoil and newspaper where there are no holes in the newspaper.
Tape the wire down so that the bare copper touches the tin foil making good contact. Make sure the copper wire makes good contact with the tin foil.
Anchor the cable to the newspaper with tape on this side.
Very carefully turn over the newspaper and foil pressure pad and secure the other wire in the cable to the other piece of tin foil. Be very careful not to tear the paper or tin foil, or crease it.
Put this assembly carefully to one side.

Making the alarm section

This section of the STEM burglar alarm is much easier to make and should only take a few moments to do. Nevertheless care is still needed.

The items needed for this stage are the battery clip and the buzzer.

There are only two stages in section of making the STEM burglar alarm.

Take the battery clip and the buzzer. Carefully twist the red wires of each together. (Normally most electronic buzzers are polarised and have one positive and one negative connection. If not, then do not worry about the polarisation).

Note: Be very careful not to stick the wires into yourself.
Cover joint carefully with tape. This prevents and short circuits.

Final assembly of the STEM project

This section of the assembly needs a little care. Make sure that the wires are not torn from the pressure pad.

Apart from this the STEM burglar alarm project is very easy to put together.

Take the tin foil and newspaper pressure pad and place it under a suitable rug.
Take the cable and join one wire to the black battery wire, and the other wire to the black buzzer wire.
Insulate and cover both wires with tape.
Plug the battery in.
Stand, but not jump on the rug.