IR Based Security Alarm Circuit

IR based security alarm circuit can detect any movement and trigger the alarm. This circuit is very useful in homes, banks, shops, restricted areas where an alert alarm is needed on any movement. This circuit is based on IR sensor where an IR beam is continuously falling on a photodiode, and whenever this Infrared beam breaks, by any kind of movement, alarm is triggered.


IR sensor consist an IR LED and photodiode, in which IR LED emits IR radiation and photodiode detects the radiation. Photodiode conducts current in reverse direction, whenever light falls on it, and voltage across it changes, this voltage change is sensed by voltage comparator (like LM358) and generates output accordingly. [Also check: IR Sensor Circuit]


In this IR based security alarm circuit, we have placed IR LED in front of photodiode, so that IR light can directly falls on photodiode. Whenever someone moves through this beam, IR rays stops falling on photodiode and Buzzer start beeping. Buzzer automatically stops after some time, as buzzer is connected to 555 timer in monostable mode.

IR Working

This kind of Alarm can also be build Laser light, (like Laser Security Alarm Circuit) but the benefit of using IR sensor is that IR light in invisible while Laser is visible. Although both are useful and have different scope.



  • IR pair (IR LED and Photodiode)
  • 555 timer IC
  • IC LM358
  • Resistor 100, 10k, 100k, 330, 220 ohm
  • Capacitor 10uF
  • Variable resistor – 10k
  • Buzzer


Circuit Diagram and Explanation

Infrared Security Alarm Circuit Diagram

We have used op-amp LM358 in this circuit, LM358 has two voltage comparators inside it, and we have used one comparator here. Non-inverting end (PIN3) of voltage comparator is connected to the Photodiode and inverting end (PIN 2) of voltage comparator is connected to a variable resistor of 10k. Output of the voltage comparator (PIN1) is fed to the Trigger pin of 555 timer. 555 Timer is configured in monostable mode here.


While the IR radiation is falling on Photodiode, the voltage at the non-inverting end (+) of voltage comparator is higher than the inverting end (-) and the output of the comparator is HIGH. And as the comparator output is connected to the trigger PIN of the 555 timer, so the when the Trigger pin 2 is high, the 555 output is low. So during the period when the IR rays falls on Photodiode, the 555 timer output remains LOW. To understand the working of IR sensor with comparator LM358 go through this article: IR Sensor Module Circuit


Now when there is some movement, the falling of IR rays on Photodiode gets interrupted and the voltage at inverting end (Threshold voltage) of voltage comparator becomes higher than non-inverting end, for some moment. This makes the output of comparator LOW and also makes the Trigger PIN 2 of 555 timer LOW. This will trigger the 555 timer, and 555 timer’s OUTPUT goes HIGH and Buzzer beeps for short duration. Duration of the beep can be increased by changing the value of resistor R1 or capacitor C1 (RC network in monostable mode of 555 timer IC). Note that 555 IC gets triggered when Trigger PIN 2 gets LOW.



  • Normally the range of IR LED is 2 meter, but it can be increased by using Lens.
  • AC alarm can be used in place of Buzzer, by using Relay.
  • IR LED and Photodiode must be properly aligned so that IR rays can directly falls on photodiode.
  • The sensitivity of the sensor can be changed by variable resistor RV1.

Comments (42)

  • QAMAR SHAIKH's picture


    Nov 25, 2015
  • KILTON ROY's picture

    sir uin rv u have used pot or not i see there is a one pot there if yes plese say

    Feb 26, 2016
  • Abhishek's picture

    RV stands for Variable Resistor, and also called POT (potentiometer), so yes RV is POT.

    Feb 27, 2016
  • walia farzana's picture
    walia farzana

    sir can we use 9 volt battery instead of 5v

    Mar 08, 2016
  • Jayant's picture

    Of course, you can use 9v battery.

    Mar 12, 2016
  • Jani Sid 's picture
    Jani Sid

    Nice guys.. Awsm project... keep it up.... congo

    Mar 09, 2016
  • Alex's picture

    I am working on this project with a friend and we cannot get it to work properly. We believe the photo diode isn't picking up the IR signal. Any feed back as soon as possible would b greatly appreciated.

    Mar 29, 2016
  • Jayant's picture

    Its a very simple circuit and should work without any issue. Try to adjust Variable Resistor or replace the component which you believe to be faulty.

    Mar 29, 2016
  • lakshmi's picture

    sir we r did this project but it nt working properly...wen we connect the buzer it get wat changes should to...pls tel

    Jul 22, 2016
  • Alex's picture

    Now we got the circuit to properly to work with a LED in place of the buzzer. However, when the buzzer is in the normal place and movement moves across the photo diode; the buzzer turns on and stays on. Any ideas?

    Mar 30, 2016
  • ruchitruchit sardhara's picture
    ruchitruchit sa...

    plz.. give me circuit with high decimal speaker

    Apr 07, 2016
  • OverpoweredAlphabet's picture

    This is very badly designed and i do not like it ONE BIT

    May 09, 2016
  • kim's picture

    Can i use LDR in replacement to photo diode??
    Im not sure but the ckt i assembled was consistently buzzing only.

    Jun 07, 2016
  • Maddy's picture

    No, you have to use Photo Diode to detect the IR radiation.

    Aug 20, 2016
  • lenin's picture

    Sir when i connect this circuit i am not getting result...the buzzer is countineously in on state....could u please help meeee

    Aug 28, 2016
  • Gautam kumar's picture
    Gautam kumar

    change polarity

    Oct 17, 2017
  • Akash's picture

    Maker's of the circuit please help us in finding a way about it.... buzzer is buzzing continuously...instead we placed a LED..same result.... Yours help will be remember forever...

    Sep 02, 2016
  • Maddy's picture

    @lenin @Akash Try adjusting the variable resistor RV1. Circuit is quite simple, just follow it, this will work for sure. Also check connections with LM358 IC.

    Sep 21, 2016
  • Deepankar's picture

    The circuit is very simple , easily done ...thanks admin keep posting more..

    Sep 12, 2016
  • harikrishnan's picture

    I did it and didn't work

    Oct 25, 2016
  • bhavana michael's picture
    bhavana michael

    nice and very easy project!!thank u jayanth

    Nov 06, 2016
  • sudara's picture

    Sir can i use tsop 1836 reciver. And how many distance work it? Plz reply me. Im from sri lanka

    Nov 09, 2016
  • Jasper's picture

    What does the variable resistor do in this circuit? i have tried to figure this out many times but I can't figure out the purpose. please help

    Nov 11, 2016
  • chiranjeevi's picture

    thank you. its working for me. I want t extend this project. Instead of using a buzzer, I want this circuit to send a sms alert. So how can I proceed.

    Nov 29, 2016
  • Champ's picture

    Did u use 5 volt or 9 volt battery

    Dec 14, 2016
  • Navya's picture

    sir, can I use IC 741 instead of of LM

    Mar 06, 2017
  • Swathi's picture

    At what distance between LED & photo diode the alarm is triggered

    Mar 07, 2017
  • Akshay Prajapati 's picture
    Akshay Prajapati

    555 timer ic is heating. So and not working circuit so you can Gide me?

    Apr 16, 2017
  • anshuman's picture

    circuit diagram is wrong thts why who made this project according to this ckt diagram will not work

    Apr 27, 2017
  • Ishaan's picture

    If I want to buy this exact kit does any know where I can do this from?

    May 07, 2017
  • tsegaye's picture

    this project is very nice so I am your aprtiater ok

    Jul 11, 2017
  • Madan's picture

    Sir,can u send the PCB design of it

    Nov 01, 2017
  • Chandrasekhar 's picture

    sir , instead of buzzer , I wanna insert relay , can I increase the time period of trigger state ??

    Dec 09, 2017
  • deepankar's picture

    yes you can do that just by changing the value of RC i.e resistor and capacitor.

    Jan 22, 2018
  • AISHA's picture

    Yes as deepakar said the value if time period can be changes by changing by RC values. Also yes you can use a relay with its driver circuit in place of the buzzer

    Jan 23, 2018
  • Ajay's picture

    Please suggest suitable values of RC and driver circuit to drive a 5V relay at the output which will be used to open a solenoid valve of a tap.

    Mar 29, 2018
  • seeker's picture

    I just noticed that the IR led has the value of 10K different from what is in the circuit which states 100 ohms only, apparently the photo diode is connected to 100 ohms instead of 10k.. ur schematic and actual photo shot of the circuit didnt match..

    that's maybe why i can't make the circuit work.
    kindly answer my query.. cheers

    Jan 23, 2018
  • B.Aswinth Raj's picture
    B.Aswinth Raj

    Its given correctly in the circuit. The one connected to IR led is 100 ohm and the one connected to op-amp is 100k

    Jan 24, 2018
  • hemant's picture

    will the beeping gets higher when the obstacle comes close?
    if no what should be done to vary the beeping as he object moves closer to the reciever?

    Feb 28, 2018

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