Door Alarm System

Link 1: Make You Own Alarm
There a possible ways of building a door alarm. This link shows how make a door alarm yourself. You can use spare items that are already around your house with addition of a few minor things needed from the hardware store. Things that are needed are as followed: Insulation, Flexi-Wire, Electrical Tape, 9 Volt Battery Holder, Electrical Buzzer, Clothes Pin, Knife, Thumb Tacks, and a ruler. First you are suppose to prepare the wires, where you have to strip a half inch on insulation of both ends of flexi wire using the knife. The insulation should hold the two wires. The 2 wires should then be attached to the metal connectors on the 9 volt battery holder. This should be secured with electrical tape. After, the wire sgould be connected to the electrical buzzer.. and both wires need to be connected to the joints of the electrical buzzer and be held securely with electrical tape. 
To check if the buzzer works properly, you would need to connect the battery to the holder. IF the proper connections are made, the buzzer should go off, and if the buzzer does not go off, the wires should be repositioned.  Once a buzzz is made officially, the batteries should be removed. Assemling the wires would consist of going down the flexi wire to about half a meter, and cutting one of the wires in half. Separate both of the wires that are within it, cutting only one of the wires. Strip down both cut wires with the knife. Opne the clothespin as normally and stick 2 thumbtacks inside the opening of the 2. this is to assure the buzzer will make noise once intact. another wire should be attached to the opposite end of the clothespin against the other thumb tack. The clothespin should then be closed and the batteries shoud be attached again.

Link 2: Super Simple Door Alarm
In this link, it provides the basics of building a door alarm system with using simple items. There are many ways to build a door alarm system. All are different design and some are uniquely or prfessionally made. What is unique about this it uses a smoke detector. The idea is to take a door contact used in alarm systems which will  then be connected to a smoke detector, and yes an on/off switch should be included. The materials needed for this door alarm are wires, smoke detector, battery, magnet contact. The plastic that protects the smoke detector should be removed as well as the pcb from the plastic shell. There should be a little metal strip next to the led, this is the test button, or the contact area. the pcb should be turned upside down and find the contacts for the switch. Here a wire of 10cm long is needed, then it should be solder to one of the test button contacts and to the other. Two wires should be loose in the end and they should be connected to the switch. A hole should later be drilled in the smoke alarm lock and the switch should be able to fit and later fastened.
Afterwards the pcb should be back in place and the lock should be back on. The Loose end of the cable should then be connected to the door contact and put the switch to on. Test it out by opening and closing the door contact, and the alarm should go off. Fianlly install on door.

Link 3: How to make a Door Alarm

 This links shows the process of making a door alarm even kids can use it. Its fairly simple and the materials needed are 2 insulated wires, 2 stripped wires, 1.5 volt battery, string 3-5 long, electrical tape, 1.5 volt mini buzzer, string type wooden clothes pin, piece of plywood 4in x 12 greater, and glue. A battery and buzzer should be placed on the wood, where the battery goes on the top right corner of the wood and battery on the top right. They should then be taped down with electrical tape. The clothes pins should later be wraped with non insulated wire (end of clothespin). The wires should touch when the clothespin are closed. Later connect one of the free ends of the wire around the clothes pin to a wore coming from the battery. The wire should then be connected around the clothes pin to the buzzer and the remaing free wire from the batter to the buzzer. The switch should be tested by opening and closing the clothes pin. The buzzer should make a sound when the switch is closed, and if not, the wiring should be checked. The piece of carboard (or any other insulative material) in the clothespin to seperate the wires. This is to keep the buzzer from not going off anymore when it clothes. The clothespin should then be glued to wood, and a string should be attached to the piece of cardboard beween the close pin. The other end of the string should then be attached to the door. The alarm should be place where the string is taut between the alarm and the door. When the door is being opened, the string should pull the cardboard out, setting off the alrm. 

Videos: (more videos will be added later using out side resources.)
http://www.teachersdomain.org/asset/phy03_vid_zalarm/