Protecting your home and family is a top priority. A laser tripwire alarm is an inexpensive, DIY way to detect intruders and alert you when someone crosses a protected boundary. With just a few electronic components and an Arduino, you can set up a laser tripwire alarm to sound an audible siren if triggered. This guide will walk you through everything you need to know to build your own laser tripwire intruder alarm for home security.

What is a Laser Tripwire Alarm and How Does it Work?

A laser tripwire alarm uses an invisible laser beam to create a protected zone around a door, window, or other area. The alarm sounds if the laser beam is broken by someone crossing it.

The alarm works by shining a laser diode across a space and onto a laser sensor on the other side. The laser diode emits a steady laser beam that is detected by the sensor. This completes the electrical circuit between the diode and sensor.

If someone crosses through the laser beam, the beam is temporarily blocked from reaching the sensor. This breaks the circuit, which triggers the alarm. Even a momentary interruption of the beam sets off the alarm.

Key Advantages of a DIY Laser Tripwire Alarm

Parts and Tools Needed to Build the Arduino Laser Tripwire

Building your own laser tripwire alarm requires just a few electronic components, basic tools, and an Arduino microcontroller board. Here's what you'll need:



I'll go over how to wire and program the components later in this guide. Having the right parts on hand will make the DIY build much easier.

How to Set Up the Arduino Laser Tripwire Circuit

The first step is to build the circuit on a breadboard that will control the laser tripwire alarm. This involves connecting the Arduino, laser diode, laser sensor, buzzer, battery, and other components.

Here is an overview of how to construct the circuit:

Refer to the wiring diagram below as an example:

Laser tripwire alarm circuit wiring diagram

Double check all connections before powering on the Arduino. Prototyping the circuit on a breadboard first makes it easy to modify as needed.

Once the hardware is tested and working, you can solder the final circuit onto a prototype PCB or perfboard for installation in the alarm housing.

Arduino Code to Operate the Laser Tripwire Alarm

With the circuit wired up, the next step is loading an Arduino sketch onto the board to control the alarm.

The Arduino code needs to:

Here are key functions the Arduino sketch should contain:

// Define pin numbers
const int LASER_PIN = 2;
const int SENSOR_PIN = A0;
const int BUZZER_PIN = 3;

// Sensor threshold voltage
const int THRESHOLD = 400;

void setup() {

// Set pin modes


void loop() {

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

// Read analog voltage from sensor
int sensorReading = analogRead(SENSOR_PIN);

// Check if beam is interrupted
if(sensorReading < THRESHOLD) {

// Trigger buzzer alarm
tone(BUZZER_PIN, 1000);

else {

// Turn buzzer off


delay(10); // Small delay


This simplified sketch outlines the key functionality needed. You can enhance it by adding features like a startup delay, alarm shutoff timeout, motion sensor, etc.

Upload the code to the Arduino board. Once running, the laser tripwire alarm will activate when you break the laser beam.

How to Align and Position the Laser Tripwire Components

To work properly, the sending and receiving ends of the laser tripwire must be carefully positioned and aligned:

Depending on the beam angle, the tripwire typically works over distances of up to around 20 feet. Wider beam lasers can cover longer ranges.

Experiment with placement in the location you want to protect. The modules can be mounted to walls, attached to brackets, or embedded into housings.

Constructing an Enclosure to House the Electronics

For permanent installation, it's important to enclose the alarm circuitry in a protective housing:

A clean looking enclosure preserves the electronics and keeps the wiring securely contained. Mount the box in an inconspicuous location within cable reach of the laser tripwire modules.

Applications and Options for Enhancing Your Laser Tripwire Alarm

A basic laser tripwire alarm provides an affordable perimeter protection system, with room for enhancements:

The core principles remain the same. By mastering the basics of the DIY laser tripwire alarm, you can springboard into more advanced projects!

So don't wait to enhance your home's protection. With an Arduino microcontroller, basic electronics components, and a weekend of effort, you can construct a custom laser tripwire alarm system tuned perfectly for your needs. The knowledge you gain will open up even more possibilities for future Arduino-based security and automation devices.