Installing car alarms are as important as installing a door locking system in your car. Homemade car alarm systems revolve around a simple concept of making a loud noise and a means of triggering it. Traditionally, alarm systems work via radio signals to trigger several other mechanisms such as alerting the police or automatic checking of locks. By following a few simple rules, you can build your own cost effective and efficient homemade car alarm system with the help of a few household items.
Use a wire stripper to remove the insulation from the wires and attach one end of the wire to the positive terminal of the battery clip and the other end to the negative terminal of the battery clip. Remove the insulation from two more wires and attach the ends of one of these to the positive terminal of the electric alarm and the other end to the negative terminal of the electric alarm.
Use glue or tape to secure the electric alarm and battery clip to the plywood. Ensure that the electric alarm and the battery clip do not touch together. These can be close but not touching.
The loose end of the wire connected to the positive terminal of the battery clip will be tied around the upper jaw of the wooden alligator clip. The loose end of the wire connected to the positive terminal of the electric alarm will be tied around the lower jaw of the wooden alligator clip. When the clip is bunged (or plugged), the bare metal parts of both the wires should come into contact.
Cut out a piece of cardboard and place between the jaws of the alligator clip to create an obstacle between the two wires. Cut out the cardboard so a considerable length should go beyond the length of the alligator clip.
At the far end of cardboard, create a hole with the help of a pin and put a small length of sturdy string through it. The hole should be made so if the cardboard is pulled out of the jaws of the alligator clip, it won't tear apart. Once the cardboard is pulled out and the two jaws connect, the alarm will be triggered.
Stick the alligator clip to the plywood using glue or electrical tape, then glue or tape this piece of plywood under the seat of your car or a convenient place where the mechanism will not be visible easily.
The piece of sturdy string going through the cardboard must be connected to the locking mechanism of the car. Tie the string around the locking mechanism so it triggers with a keyless entry. Insert batteries into the battery clip and test your alarm to make sure it works.