How to Make a "Laser Security Alarm System" at Home on a Breadboard.




Introduction: How to Make a "Laser Security Alarm System" at Home on a Breadboard.

About: Hi. I'm Troy Araujo and welcome to my page. I upload content related to simple electronic projects, home made things, DIY tutorials, breadboard circuits, life hacks and much more. My YouTube channel name is T…

In this tutorial I will show you how to make your own "Laser Security Alarm System" or a "Laser Sensor" on breadboard in just a few steps.

Step 1: Gathering the Required Electronic Components

The components you will require for making this circuit are as follows:-

COMPONENTS REQUIRED:- LDR (Light Dependant Diode)

L.E.D (Light Emitting Diode)

BC547 Transistor (1)

100 ohm or 330 ohm resistor (1)

Buzzer (1)

9v Battery with holder


You can get all these components easily from any electronic shop or from online sites like Amazon,E-Bay etc.

Step 2: Circuit Diagram

This is the circuit diagram of our "Laser Alarm System."

Step 3: Steps for Construction of the Circuit

The BC547 Transistor has 3 pins. When the flat side is facing you that time the 1st pin is called the collector, the 2nd pin is called the base and the 3rd pin is called the emitter.

now lets get started;

1. Place the BC547 Transistor on the breadboard.

2. Then connect the LDR from the base and emitter of the BC547 Transistor.

3. Now connect one end of the 330/100 ohm resistor to the base of the BC547 Transistor and the other end of the resistor to a blank space on the breadboard.

4. Connect the anode of the L.E.D to the resistor and the cathode of the L.E.D to the collector.

5. Connect the buzzer in the same way you connected the L.E.D.

6. Now connect the Battery; positive side of the battery to the resistor and negative part of the battery to one side of the LDR

Step 4: Testing the Laser Sensor

As soon as you connect the battery the L.E.D and buzzer will come "ON" (if you're in a dark room). Focus the Laser diode/light on the LDR and you will see the L.E.D and Buzzer going "OFF" If you interrupt the laser light focusing on the LDR the circuit will trigger and the alarm will ring!

Congrats! Your "Laser Security Alarm System" is now ready! Enjoy!

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1 Person Made This Project!


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Question 2 years ago

can the circuit be modified for using hooter which works at 230v instead of buzzer.
Can the circuit be modified to give continuous sound once the light beam is obstructed?


Question 4 years ago on Step 1

can i use 150 k ohm resistor


Question 3 years ago on Step 3

Can I use Pcb instead of bread board


3 years ago on Step 3

Please could u indicate the led and buzzer in the circuit diagram?


5 years ago

I like the project, I'd like to build something the requires (3) lasers, this way I can establish direction of movement and duration of stay. I'd like your help in building this project if you have the time and we can establish bill of materials. I'm level 3 solder have tools to work with.



door way sensor.png

5 years ago

LDR means light dependant resistor. They are sensible to any light length, including daylight, I think an IR detector would better suit you needs.


5 years ago

I need one of these for the animals trying to sneak into the kitchen XD