IR Based Security Alarm


ByJayant 49

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.


Get Our Weekly Newsletter!

Subscribe below to receive most popular news, articles and DIY projects from Circuit Digest


  • KILTON ROY's picture
    Feb 26, 2016

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

  • Abhishek's picture
    Feb 27, 2016

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

  • walia farzana's picture
    walia farzana
    Mar 08, 2016

    sir can we use 9 volt battery instead of 5v

  • Jani Sid 's picture
    Jani Sid
    Mar 09, 2016

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

  • Alex's picture
    Mar 29, 2016

    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.

  • Jayant's picture
    Mar 29, 2016

    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.

  • lakshmi's picture
    Jul 22, 2016

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

  • Alex's picture
    Mar 30, 2016

    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?

  • ruchitruchit sardhara's picture
    ruchitruchit sa...
    Apr 07, 2016

    plz.. give me circuit with high decimal speaker

  • OverpoweredAlphabet's picture
    May 09, 2016

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

  • kim's picture
    Jun 07, 2016

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

  • Maddy's picture
    Aug 20, 2016

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

  • lenin's picture
    Aug 28, 2016

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

  • Gautam kumar's picture
    Gautam kumar
    Oct 17, 2017

    change polarity

  • Akash's picture
    Sep 02, 2016

    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...

  • Maddy's picture
    Sep 21, 2016

    @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.

  • Deepankar's picture
    Sep 12, 2016

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

  • harikrishnan's picture
    Oct 25, 2016

    I did it and didn't work

  • bhavana michael's picture
    bhavana michael
    Nov 06, 2016

    nice and very easy project!!thank u jayanth

  • sudara's picture
    Nov 09, 2016

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

  • Jasper's picture
    Nov 11, 2016

    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

  • chiranjeevi's picture
    Nov 29, 2016

    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.

  • Champ's picture
    Dec 14, 2016

    Did u use 5 volt or 9 volt battery

  • Navya's picture
    Mar 06, 2017

    sir, can I use IC 741 instead of of LM

  • Swathi's picture
    Mar 07, 2017

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

  • Akshay Prajapati 's picture
    Akshay Prajapati
    Apr 16, 2017

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

  • anshuman's picture
    Apr 27, 2017

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

  • Ishaan's picture
    May 07, 2017

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

  • tsegaye's picture
    Jul 11, 2017

    this project is very nice so I am your aprtiater ok

  • Madan's picture
    Nov 01, 2017

    Sir,can u send the PCB design of it

  • Chandrasekhar 's picture
    Dec 09, 2017

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

  • deepankar's picture
    Jan 22, 2018

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

  • AISHA's picture
    Jan 23, 2018

    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

  • Ajay's picture
    Mar 29, 2018

    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.

  • seeker's picture
    Jan 23, 2018

    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

  • Aswinth Raj's picture
    Aswinth Raj
    Jan 24, 2018

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

  • hemant's picture
    Feb 28, 2018

    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?

  • jayanth kumar's picture
    jayanth kumar
    Aug 28, 2018

    this will for ac voltage .

  • Aswinth Raj's picture
    Aswinth Raj
    Aug 29, 2018

    No, if you want to power with AC mains use a adapter which will convert 220AC to 12V or 5V

  • Mohammed Abdul Aziz a lameen's picture
    Mohammed Abdul ...
    Aug 29, 2018

    What should I do if I want the circuit to be effective if I have a distance of 20 meters ? Can I separate the IR LED from the receiver section ? Yes Sir.

  • Mohammed Abdul Aziz a lameen's picture
    Mohammed Abdul ...
    Sep 02, 2018

    How can we practically increase the distance coverage of this circuit ?

  • Mohammed Abdul Aziz a lameen's picture
    Mohammed Abdul ...
    Sep 08, 2018

    I am getting no answers to my questions.I have noticed resister 330 ohm among components list .It does not show on the schematic.kindly clarify this.How do you approve questions ?Thank you Dir.

  • Aswinth Raj's picture
    Aswinth Raj
    Sep 12, 2018

    Follow the circuit diagram for making connections and selecting component values. I am not sure where you spotted a 330 ohm resistor only a 220 resistor is used for speaker.

    Also you can use the forums for technical help and it is much active than comment section 

  • Thomas A's picture
    Thomas A
    Apr 04, 2021

    Hello, I copied your circuit but my problem is that buzzer keeps on beeping. Can anyone help me?


Log in or register to post Comment