It can be easy to make your own door alarm. Finding everyday parts that are already laying around your home and a quick trip to the hardware store will give you everything you need to build your own security device. This is also much simpler and more affordable than using an alarm company with professional installation.
Strip a ½-inch of insulation off both ends of Flexi-wire using the knife. The insulation should hold two wires. Take the two wires, and attach them to the metal connectors on the 9-volt battery holder. Secure them with pieces of electrical tape. Connect the other wire to the electrical buzzer. Both wires need to be connected to the joints of the electrical buzzer and held there securely by using electrical tape.
You can then check to see if it works properly by connecting the battery to the holder. You will hear the buzzer go off if you have made the proper connections. If you do not hear the buzz, reposition the wires. Once you hear the buzz, remove the batteries.
Assemble the Wires
Go down the Flexi-wire to about half a meter, and cut one of the wires in half. Separate both wires that are within it, and cut only one of the wires. Strip down both cut wires with the knife; try not to knick the other cut of the Flexi-wire. Strip about one centimeter each. Set this aside.
Open the clothespin as you normally would, and stick two thumbtacks inside the opening of the two. The tack heads have to come in contact with each other. Do not push them down all the way yet. This is to ensure the buzzer will sound once it is completed. Take the two stripped wires, take one side of the wire, and place it underneath the thumbtack. Press it down firmly so the wire is secure as well.
Attach the other wire on the opposite end of the clothespin, against the other tack. Make sure to press firmly to secure the wire and the thumbtack against the clothespin. Close the clothespin, and attach the batteries back to the holder. The buzzer should sound if everything is in place correctly. Reset the wires if there is no buzzer. Open the clothespin, and place it onto the doorframe. When the door shuts, the two thumbtacks should not touch. When the door opens, the tacks will then come into contact.
Attach the rest of the assembly to the back of the door. Check the alarm from time to time to ensure it is working properly. Secure the assembly to the back of the door using tape or string to ensure it will not move.