Homemade Door Alarm

Basics

• All burglar alarms require three elements: a trigger, a power source and a noise-making device such as a bell or buzzer. A do-it-yourself door alarm just needs something to set the buzzer off when the door is opened and a buzzer loud enough to alert anyone nearby.

Equipment

• A homemade door alarm requires a battery (held in a battery pack) to power the buzzer and a mini alarm. Both can be purchased for a few dollars at outlets like Radio Shack. You also need four pieces of insulated wire to connect the buzzer and battery to each other and elements to create the trigger: a length of string, a piece of cardboard, a spring-loaded wooden clothes pin, a little tape or glue and a thin wooden board on which to mount the buzzer.

Assembly

• Start by stripping the insulation from the ends of two lengths of wire. Then wrap the end of one wire around the top jaw of the clothes pin and the end of the other wire around the bottom jaw. When the pin is closed the two wires should touch. Place the piece of cardboard between the jaws, keeping the wires apart; when the cardboard is yanked away it will complete the circuit and set off the buzzer. Take the other end of one wire and connect it to the positive terminal of the buzzer and the other to the negative terminal of the battery pack. Then connect the positive terminal of the battery pack to the negative terminal of the buzzer. Mount them on a board and secure them with tape or glue, then put the battery in the battery pack. The burglar alarm is now set.

Mounting

• When using this assembly for a door alarm, you want the act of opening the door to yank the cardboard away. You can do this by taping or gluing the board containing the alarm assembly to a spot on the wall near the door. Then punch a hole on the end of the cardboard with a pin, run a string through it and tape the string to the top corner of the door farthest from the hinges. Make sure the string is short enough to pull the cardboard free when the door opens. When it does, the alarm will go off--waking you up, scaring away the burglar and keeping your possessions safe.