Do you not like your parents opening door without knocking? Let’s make simple alarm system for your room that will warn you from everyone who is about to enter your room!!
What you need:

1 – 9V battery
1 – 12v dc buzzer (Available at Radio Shack or amazon)
1 – Aluminum foil (Available at Walmart)
1 – paper tape
1 – scissors
1 – foam board
1 – knife
1 – Dishing washing sponge

## Step 1: Prepare What Is Needed

Prepare all the materials that is needed to make

Under is estimated cost for materials:
12V dc battery - \$1.50
12V dc buzzer \$ 3.5
Paper tape - \$1.5
Hard board \$1.5

## Step 2: Testing Battery and Buzzer

Hook the battery to the buzzer and make sure the buzzer is working fine as well as the battery.(I hooked + side of the battery to red wire but it is not necessary)
Test it out by just making the wire from 9V DC battery that is not hooked to buzzer touch the other wire of the buzzer.
If it makes buzzer go then buzzer and battery is working.

## Step 3: Cutting the Foam Board

Cut the hard board into size that is little bit smaller for the size of a door mat that one has.
(Usually about 20 x 24 inches work fine for most of the door mats.)

## Step 4: Cutting Aluminum Foil Into Right Size

Cut the aluminum foil with same length as the foam board (you will put aluminum foil attached to each side of the foam board later).

## Step 5: Drawing 3 Circles

Measure the length of the foam board to mark the center of the holes.
To figure out the exact measurement, the radius of the holes should be 4 inches less than the length of the foam board(There will be three holes and they will be apart by 1 inch including the edges.) then dividing that by 3 will give you the length of the radius that should be used for the hole.

First draw a center line where all the center of the holes will be located at. Then mark the center of the hole and draw a circle with the radius obtained with a compass. Measure 1 inch from each of the dots where center line and the center circle meets and from that measure the radius obtained and place the dots for other 2 holes.
With compass draw 2 circles with the 2 center dots previously marked

## Step 6: Cutting the Holes With Knife

Cut the holes with knife.
Using scissors would help to cut the foam board faster.

## Step 7:

Attach one aluminum foil that is prepared previously to one side of the foam board. Make sure it stays constant and tight.

## Step 8:

Cut dish washing sponge in to 3 even separate pieces.
Attach each 3 pieces of the sponge to middle of each 3 aluminum foils that is seen through the hole. (Either tape and glue will work.)

## Step 9: Attaching Top Part of Aluminum Foil

Attach the other side of the foam board with the left aluminum foil.
(Make sure aluminum foils do not touch each other from each side.)

## Step 10: Attaching the Buzzer and Battery

Now attach one side of the buzzer wire to the battery with a paper tape. (It does not matter which side)
Attach the not attached part of the buzzer to the top aluminum foil which is on top of the sponge with paper tape.

Attach the other part of battery wire that is not attached to the bottom part of the aluminum foil.

## Step 11: Checking Process

Press the aluminum foil on top to make both top and bottom aluminum foil get attached and make sure the buzzer still works.
(If it does not work check whether aluminum foil is ripped or wire is attached right.)

## Step 12: Put the Board Under the Doormat

If everything is working put it under the doormat where people enter and step on it. If it works then you have a warning alarm system that will warn you whenever someone is about to enter. I would put the battery and buzzer inside the room so it would camouflage better.