How to Make Your Own Door Alarm

Strip about 1 centimeter of insulation off of both ends of the flexi-wire with a sharp knife. Within the insulation, there should be two wires.

Take the two now-exposed wires and attach them to the metal connectors of the 9 volt battery holder. To hold them in place, use the electrical tape to attach them.

Connect the other end of the flexi-wire to the electrical buzzer. The two wires attached to the metal connectors in Step 2 need to be connected to the two joints/connectors of the electrical buzzer. Connect them securely with electrical tape.

Check to see if everything is working by connecting the battery to the holder. If the alarm buzzes, you have created a proper circuit, and all is correct so far. If the alarm doesn't buzz, reposition the wires, making stronger connections, and try again. Once you get it working, take the battery out.

Measure down half the length of the flexi-wire (to about half of a meter) and cut one of the internal wires in half. Flexi-wire is made in such a way that it looks as if you stuck two individually insulated wires together to form one wire. You should see the separation of the two wires easily. Cut only one of the wires.

Strip the two freshly cut ends of the wire with your knife, making sure not to nick or scratch the other half of the untouched flexi-wire. Strip them to about 1 centimeter each and set the whole assembly aside.

Open the clothes pin normally and stick the two thumb tacks into the inside of the opening so that when you let the clothes pin close, the two thumb tack heads will come in contact with each other. This will close the circuit and allow the buzzer to sound once the wires are connected. Place them inside the clothes pin but don't push them down completely yet.

Take the two open ends of the wire that you stripped in Step 6 and place one side of the wire underneath the head of the thumb tack. It should now be between the thumb tack and the clothes pin. Once it's in place, press the thumb tack down securely and forcefully so that it holds the wire secure.

Attach the other end of the cut wire from Step 6 into the space between the other thumb tack and the opposite side of the clothes pin. Repeat the same process from Step 8, making sure it is secure.

Let the clothes pin close and attach the battery to the holder. If all the connections are in place, the buzzer should sound. If the wires are not in place or not set up properly, retest all the connections and redo them if necessary.

Open the clothes pin and place the squeezable ends into the doorframe of the door you wish to alarm. Stick it in there so that when the door is shut, the two thumb tacks aren't touching; but once the door opens, the clothes pin will spring shut, touching the tacks, completing the circuit and causing the buzzer to sound. Attach the entire assembly to the back of the door, or wall surrounding the door, with tape or staples.

Check on the alarm from time to time to insure that it's functioning properly. If you notice that the alarm is too sensitive or doesn't always work properly, you can add a piece of cardboard between the tacks. Attach the cardboard to a string and attach the string to something that won't move. That way, when the door opens, the cardboard won't be able to follow and will slide out of the clothes pin, closing the circuit.