How to Make a Simple Alarm
This is about the simplest electronic alarm that you can make. When someone enters the room the door opens, an iron plate attached to one part of the circuit contacts a magnet attached to another part, effectively functioning as a switch and completing the circuit. To deactivate the circuit, all you have to do is pull the magnet off of the metal plate and set it down in front of the door again. Not the most secure or even the most elegant solution, but definitely the simplest! Does this Spark an idea?
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Things You'll Need
- Insulated copper wire
- Soldering iron
- Solder
- Buzzer
- Neodymium magnet
- Iron plate
- Tape
Instructions
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1
Stock up on supplies. Note the voltage on the buzzer. The power supply needs to provide as close to the voltage required by the buzzer as possible without going over. For example, an 8.7 volt buzzer will work fine with an 8 volt power supply, but could be damaged by a 10 volt one. Amperage is a different matter. Your power supply should output at least as much amperage as the buzzer calls for, if not more.
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2
Connect one terminal of the buzzer and one terminal of the power supply together. Solder the connection to make it permanent.
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3
Figure out where you want to put the buzzer and power supply in the room. They will need to be close enough to a wall socket for you to plug them in, and out of the way so that they won't be stepped on. You might want to attach the buzzer to a wall so keep it safely out of the way.
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4
Cut out your switch wires. You want two wires long enough to reach from the open terminal of the power supply and the open terminal of the buzzer to the door with a few feet to spare. Solder them on to the terminals.
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5
Attach one of the wires to a small iron plate and the other to a neodymium magnet. It does not matter which wire is soldered to which object.
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6
Mount the plate on the foot of the door and place the magnet several inches inside the door. When the door is opened, the magnetism will latch onto the iron plate, completing the circuit.
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7
Place the neodymium magnet right in front of the door, just far enough away that it does not latch on to the iron plate. As soon as the door is opened, the neodymium magnet will stick to the iron plate, completing the circuit.
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Tips & Warnings
There are other ways to trigger this circuit. For example, you could attach the iron plate to the top of the door and hang the magnet from the ceiling so that it is in front of the iron plate.
This alarm can also be used to detect windows opening. Attach a small iron plate to the top of the window and hang the magnet above it.
You may wish to protect the buzzer by putting it in a box or case.
Deactivate the alarm carefully. Pulling on the wires will just pull them off of the magnet and metal plate. The best way to do this is to gently slide the magnet off the plate without unnecessarily straining the wire.
