How to Build an Alarm

Having alarms hidden around the house can make a person who lives alone feel a little more secure. Alarms can also be a big help to the parents of toddlers. Toddlers are always getting into something, especially when mom is in the shower or taking a nap. You don't need to spend a lot of money to have some simple alarms around the house. You can build an alarm yourself. You may even already have all the supplies that you need.

Difficulty: Moderate

Instructions

Things You'll Need:

• Piece of stiff cardboard, 4 inches by 8 inches
• Piece of stiff cardboard, 1 inch by 1 inch
• 2 Pieces of coated wire about 8 inches long
• 9-volt battery
• 9-volt battery harness
• Scissors
• Clothespin
• Clear duct tape
• Electrical tape
• Hole punch
• Fish line
• Buzzer, old toy, doorbell, smoke detector with test button
• Super glue

1. 
   Attach the battery harness

   Attach the battery harness to the 9-volt battery and then tape the battery to one end of the larger piece of cardboard.

2. Strip less than an inch of the plastic coating from both ends of each of the two wires and from the ends of the wires on the wire harness.

3. 
   Wrap the wires around the clothespin

   Wrap the exposed end of one wire around a clothespin so that when you are not squeezing the clothespin, the wire touches the other side of the clothespin. When you squeeze the clothespin, the wires do not touch. Wrap the exposed end of the second wire around the other side of the clothespin. When you are not squeezing, the wires should touch each other.

4. 
   Glue the buzzer and closepin to the cardboard

   Glue one of the flat sides of the clothespin to the cardboard and glue the buzzer to the cardboard using super glue.

5. Connect one the wire from the 9-volt battery to one side of the buzzer by wrapping the exposed wire around the screw.

6. Twist one of the exposed ends of a long piece of wire together with the available wire coming from the battery. Wrap the twist with electrical tape to keep it secure.

7. 
   The buzzer goes off when the circuit is complete.

   Attach the exposed end of the long wire that you just twisted and taped together to the other side of the buzzer, by wrapping the exposed end around the screw. This completes the circuit so the buzzer should sound. A light bulb is used to demonstrate the buzzer because you cannot hear the buzzer.

8. 
   Punch holes in the small piece of cardboard.

   Punch a hole in each end of the small piece of cardboard.

9. 
   The alarm stops when the circuit is interrupted by the cardboard.

   Tie two long pieces of fish line, one through each hole. Squeeze the clothespin open and then place the small piece of cardboard inside and let go. The alarm should stop buzzing.

10. Decide which door or window you want the alarm attached to and then tape the piece of cardboard to the wall and hide it under a picture.

11. Tie the fish line without slack to a door. If another door isn't too far away, tie the other piece of fish line to that door or secure the fish line near the top of the door with clear duct tape. When the door opens, the cardboard will jerk out of the clothespin. The wires will touch and the alarm will sound.

Tips & Warnings

• Try using several types of alarms for the best security. Examples are pressure alarms under rugs, door alarms and motion detectors.
• Once your smoke detector is made into an alarm it will not warn you of a fire. You will need a working and installed smoke detector.

Resources

• How a Burglar Alarm Works
• You Build It Door Alarm
• Fun Experiments Door Alarm
• Super Simple Door Alarm