How to Build a Simple Arduino Laser Tripwire Alarm That Will Keep Your Treasures Safe from Intruders

Building a simple laser tripwire alarm with an Arduino is a great way to detect intruders and keep your valuables safe. With just a few common electronic components, you can set up a system that will sound an alarm when the laser beam is broken. Here is a step-by-step guide on how to build your own Arduino laser tripwire alarm.

Gather the Required Components

To build the alarm, you will need:

• An Arduino board - This serves as the brain of the alarm system. An Arduino Uno works well.

• A laser diode module - This projects the laser beam across the tripwire path. Get one with an included driver circuit.

• A laser diode holder - This mounts and positions the laser diode. Make sure it fits your module.

• A photoresistor - This sensor detects when the beam is broken. A 10kOhm resistor works well.

• A buzzer or speaker - This sounds the alarm when the tripwire is triggered. Pick a loud one.

• Jumper wires - For connecting the components to the Arduino. Get a variety pack.

• Breadboard - To easily prototype the circuit connections. Get a 400-hole board.

• 9V battery - To power the Arduino and other components. Get a 9V battery clip too.

• Box or enclosure - For housing the electronics. A plastic project box works.

• Mounting hardware - To mount the laser and photoresistor. Get brackets, stands, tape, etc.

Assemble the Laser Diode Holder

To position the laser beam across the tripped path, you'll need to build a holder. Here are some options:

• Use a laser diode mount with a bracket or stand. This gives precise positioning.

• Glue or tape the diode into a tube or pipe. Use set screws to adjust the angle.

• Mount the diode in a pen or pencil using tape. The pressure clip can hold it in place.

Position the holder so the beam will shoot across the area you want to protect at an optimum height to detect intruders.

Connect the Laser and Photoresistor

Use jumper wires to connect:

• Laser positive lead to Arduino 5V pin
• Laser negative lead to Arduino GND pin
• Photoresistor one lead to Arduino A0 pin
• Photoresistor other lead via resistor to Arduino GND

The resistor prevents too much current flowing to the sensor. A 10k resistor is a safe value.

Add the Buzzer and Power Source

Again using jumper wires:

• Connect buzzer positive to Arduino pin 9
• Connect buzzer negative to Arduino GND
• Connect 9V battery positive to Arduino Vin pin
• Connect 9V battery negative to Arduino GND

Later you can power the Arduino via USB while testing.

Install the Arduino Sketch

Upload this sample code to your Arduino board:

```cpp
const int buzzer = 9;
const int sensorPin = A0;

void setup() {
pinMode(buzzer, OUTPUT);
pinMode(sensorPin, INPUT);
Serial.begin(9600);
}

void loop(){

int sensorValue = analogRead(sensorPin);

if (sensorValue < 400) {
digitalWrite(buzzer, HIGH);
}
else {
digitalWrite(buzzer, LOW);
}

delay(500);

}
```

This will sound the alarm when the photoresistor detects a drop in resistance as the beam is broken.

Align and Test the Tripwire

Carefully align the laser beam across the protection area and onto the photoresistor. Break the beam and ensure the alarm is triggered. Adjust sensitivity as needed via the sensorValue threshold.

Enclose the Electronics

For a finished product, mount the components neatly into an enclosure. Align the laser and photoresistor on the box edges. Secure the Arduino, wires, and breadboard inside.

Now your valuables have an Arduino laser tripwire alarm protecting them! Customize it more by adding an LED indicator, remote control, camera module, or sending you an SMS text alert.