Arduino – Laser Tripwire Alarm System

Hello everyone,

In this instructable, we will be building a laser guided tripwire alarm system using a development board.

Step 1: Parts

Arduino – Laser Tripwire Alarm System

Components used in this project:

Development board – SainSmart Leonardo R3

Enclosure – Junction Box

Trip wire – Red Dot Laser Diode

Alarm – Buzzer

Sensor – Photoresistor

Power supply – 9v battery

Wire – Male to Female Breadboard Jumper cable

Resistor – 10k

I used an improvised laser diode that was placed on a breadboard that was powered by a 9V battery. Alternatively, a laser pointer will also work well for this project.

Step 2: Assemble

Using a soldering iron, I made two horizontal holes on the junction box to house the photoresistor.

After threading the photoresistor through the junction box, I glued a piece of plastic around it.

This makes it easier to calibrate the sensor in various lighting conditions.

The positive pin from the loudspeaker connects to pin 13 on the development board.

The negative pin from the loudspeaker connects to pin 11 on the development board.

Step 3: Wiring

The photoresistor connects to the 5v pin on the development board.

The remaining pin connects to the analog 0 pin.

A connection between the analog 0 pin and the ground (GND) pin is also established using a 10k resistor.

Before placing the 9V battery inside the enclosure, I used double sided tape to separate it from the development board.

Step 4: Code

int PR = 0; //Analog 0 to Photoresistor
int Loud = 13; //Pin 13 to Loudspeaker

void setup() {

pinMode(PR, INPUT); //Photoresistor is set as an input

pinMode(13, OUTPUT);

pinMode(11, OUTPUT);

Serial.begin(9600);//set serial monitor at 9600 baud


void loop() {

int Read = analogRead(PR);// “Read” reads analog0 data

Serial.println(Read);// Print that data

if (Read < 120) //if the value is less than 120 (this can be modified based on your lighting condition),

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This Post / Project can also be found using search terms:

  • arduino alatm system project
  • laser tripwire alarm
  • arduino laser alarm
  • arduino laser tripwire using laser pointer

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