Door Alarm

Here's a nifty buzzer circuit that makes a super alarm. This is known as a contact alarm for reasons you'll soon see.

As you build this Project, you'll notice that there's no switch to turn it off or on, nor is the Key used. When you finish, touch the two exposed metal ends of the long wires together.

You'll hear a buzzer sound from the Speaker. You can use this Project to let you know if something moves and causes the two long wires to make contact with each other. For best results, place the wires so that one is horizontal while the other is vertical. This way they're more likely to make contact with each other.

You can place the long wires on a door and its frame so that they make contact when the door is closed. You can use this same arrangement for desk drawers, storage chest covers, cabinets, etc. If you need longer wires, see your local Radio Shack store for extra wire. You can also use this circuit as a Morse code practice unit by attaching the two long wires to the Key.