Home alarm systems are based around a very simple system: a loud noise and a means of triggering it. Fancy home alarm systems use radio signals to keep multiple components online and can enact numerous safety measures such as alerting the police or medical services. By applying the core principles, you can make an effective homemade alarm system with just a few household components. The sum cost is typically less than $10 per alarm.
Count the number of entryways on the ground floor of your home. This includes doors, windows, and alternate access points such as cellar doors. An effective alarm system will protect every one of these entryways.
Remove the insulation from the tips of two lengths of wire. Connect them to the positive and negative terminals on a battery clip.
Repeat the process with two more pieces of wire. This time, connect them to the positive and negative terminals of a 1.5 volt electric alarm buzzer.
Attach the battery clip and the buzzer to a small piece of plywood using glue or electrical tape.
Take the wire connected to the positive terminal on the battery clip and wrap the loose end around the top jaw of a wooden alligator clip. Then wrap the loose end of the wire connected to the positive terminal of the alarm around the bottom jaw of the clip. When the clip is closed, the exposed metal of both wires should come into contact.
Place a piece of cardboard between the jaws of the alligator clip, such that it prevents the two wires from touching. A significant length of the cardboard should stick out beyond the length of the alligator clip.
Punch a hole in the length of cardboard with a pin and run a length of string through it. The hole should be close enough to the center of the cardboard to allow you to yank it out of the alligator clip without tearing the cardboard.
Secure the alligator clip to the plywood with glue or electrical tape, then tape or glue the plywood to the door or window.
Tape the free end of the string to the door or window frame. When the door or window opens, it should pull the cardboard from from the alligator clip. That will cause the two wires to connect, completing the circuit and sending electricity to the buzzer.
Place a battery in the battery clip and test your alarm to make sure it works.
Repeat the process with every entryway in your home that you wish to secure.