How to Make a Simple Security Alarm

The problem with a simple security alarm is that security is not always compatible with simplicity. This alarm will make a buzzing sound when it is activated and nothing more. It is easy to deactivate, which makes it convenient, but not especially secure. It will reliably produce a buzzing sound when its triggered, which is enough for many applications. Basically, this alarm is good for a heads-up when someone comes in your door.

Neodymium magnet
Iron plate
Tape
Insulated copper wire
Soldering iron
Solder
Buzzer
Power supply
Box

Instructions

- 1
  Get a buzzer and a power supply. The buzzer should be low voltage, and the power supply should match the voltage and meet or exceed the amperage demands. For example, if your buzzer needs 6 volts of power and 50 milliamps, use a power supply that provides 6 volts at 50 or more milliamps.
- 2
  Attach one terminal of the buzzer to one terminal of the power supply. For most buzzers, it will not matter which terminal is connected to positive and which to negative.
- 3
  Mount your power-supply-buzzer assembly somewhere. Put it in a corner where it won't be stepped on, or mount it on the wall. You may want to put it in a box to protect it.
- 4
  Cut two long pieces of wire to reach from the remaining two terminals to the door you want to secure. Solder one to the open power terminal and the other to the free terminal on the buzzer. Make sure they are long enough to leave several extra feet once they get to the door.
- 5
  Solder the free end of one wire to a small, rectangular iron plate. It should be about 2 inches or so on each side. Attach the free end of the second wire to a neodymium magnet.
- 6
  
  Mount the iron plate in the corner of the door so that it swings out just above the ground. Place the neodymium magnet in the path of the iron plate. Plug in the circuit. When the door opens, it will complete the circuit, causing the buzzer to sound.

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