Building your own laser tripwire alarm using an Arduino and laser diodes is a fun electronics project that can be customized to suit your needs. With just a few common components, you can create a clever intruder detection system to secure your home or workspace.

What You Will Need

To build the laser tripwire alarm, you will need:



How a Laser Tripwire Alarm Works

A laser tripwire alarm uses a laser beam and photosensor to detect when the beam path is broken. Here is how it works:

So breaking the beam path with your hand, body or another object interrupts the sensor's reception of the laser and sets off the alarm. This creates a virtual tripwire across any entry point.

Constructing the Laser Tripwire Circuit

The circuit for the laser tripwire alarm contains just a few components connected to the Arduino.

Here is how to build the circuit:

1. Connect the laser diode

2. Connect the photoresistor

3. Connect the buzzer

4. Power the Arduino

This powers the Arduino when the tripwire is in use.

Once constructed on a breadboard, the circuit can be transferred to a soldered prototyping board for permanent installation.

Programming the Arduino Laser Tripwire

With the circuit complete, the Arduino code brings everything together.

The code performs the following key functions:

Here are the key steps in the Sketch:

// Define pin connections
const int laserPin = 3;
const int buzzerPin = 9;
const int sensorPin = A0;

// Threshold for triggering alarm
int threshold = 400;

void setup() {

pinMode(laserPin, OUTPUT);
pinMode(buzzerPin, OUTPUT);


void loop() {

// Read photoresistor value
int sensorReading = analogRead(sensorPin);

// Turn on laser
digitalWrite(laserPin, HIGH);

// Check if tripwire is broken
if(sensorReading < threshold){

// Buzzer on
tone(buzzerPin, 1000);


// Buzzer off 


delay(10); // Small delay


This code continuously loops through reading the sensor, checking the value, and triggering the alarm as needed. Upload it to the Arduino and adjust the threshold as needed.

Setting Up the Laser Tripwire

Once the circuit is complete and coded, you just need to properly setup the laser beam path:

With everything aligned, your DIY Arduino laser tripwire alarm should function perfectly! Position it across doorways or windows to know the instant someone crosses your virtual tripwire.

Safety Tips for Laser Tripwires

Laser tripwires use bright, focused beams of light, so its important to keep safety in mind:

Following basic laser safety practices allows you to build a secure tripwire alarm while avoiding potential hazards.

With the right components and a bit of coding, you can construct your own clever laser tripwire alarm with an Arduino. Position it across doorways or windows to detect intrusions or build sophisticated systems to protect larger areas. The possibilities are endless for enhancing security using this versatile invisible beam.