Motion detector alarm circuit with PIR sensor

You have a private area, right? If you have this motion detector alarm circuit. It will reduce your worries. Imagine a big bear is coming to the behind of your house. Then, the siren alert. The big bear is shocked and runs away. You and your family are safe. Is it great? I know you like me show simple circuits. You can do easy. This circuit is a piece of cake for you.

How it works

The basic principle, when a human or warm-blooded animal comes to a radius of about 3 to 5 meters. This circuit detects infrared radiation from theirs and sends an alarm. Infrared PIR Human Motion Sensor Detector
When a signal from an Infrared PIR Sensor module comes to the circuit. It is a 3V peak voltage. Then, this voltage flows to the base of Q1 through R1-current limiting for the transistor. Now Q1 runs, the current can flow from the 12V to a relay coil. The RY1 pulls contact C to NC. Next, the siren alert with a lot of louder. In the same time, LED glows up. Because some currents from the emitter of Q1 flows to LED. And R2 limits current to LED1. We want to use an inexpensive circuit. So, we use C1 and D1 use delay time of siren alert for 20 seconds. The S1-switch on-off the relay circuit. When you want to close a siren. Also, you can use a remote control instead of S1. When PIR Sensor runs, it will give a very short signal. We need to keep this voltage with a capacitor. And Diode-D1 protect a discharge voltage of C1, not reverse to PIR sensor. And in a signal of the output of the PIR sensor is AC form with negative voltage. So, diode rectifier to positive only can come to the trigger the transistor. It is good. Now we have a smart module. It has a delay time mode inside. But it may be expensive a little. We should use a good power supply at 12V. Although, the module has regulated supply inside. But some one may not have it. The battery 12V is a good choice.

What is a PIR sensor?

Some called Human Detector module. PIR stands for Passive infrared. It is one type of electronic device. It detects infrared radiation from an object. Through the optical integration device into a “Pyro Electric” inside. They will convert the heat energy from infrared radiation into electrical energy. Although, a little Infrared, PIR also can detect infrared and temperature waves. The manufacturer creates a PIR Motion Sensor module. They are a type of sensor device that is used to detect infrared radiation from human or animal movements. Makes we can use a PIR sensor in many applications. For example, To detect the movement of an organism or detect intrusion in security work. Infrared PIR Human Motion Sensor Detector Modules Cr: Impage by Gowoops

How to build the circuit

I try to make this circuit as easy as possible. Everything may not be as good as a hundred percent. Many friends test this circuit. It works well. Hassan bassari said. I have made this circuit successfully for my 4th-semester mini project… Please note the following to make it work…
  • Do not use the capacitor C1… as it delays the relay to activate
  • Use a 6v relay for better performance
  • It is better if we use a 12v 1A rectifier for input voltage

Parts list

  1. Q1: BC337, 0.6A 50V NPN transistor
  2. D1: 1N4148, 75V 150mA Diode
  3. D2: 1N4007, 1000V 1A Diode
  4. R1: 1.2K to 2.2K, 0.25W Resistor
  5. R1: 1K, 0.25W Resistor
  6. LED1: LED, Red 3mm LED
  7. C1; 220uF 25V, Electrolytic capacitor
  8. RY1: Relay, 6V to 9V coil
  9. PIR-Sensor: Infrared PIR Human Motion Sensor Detector Modules
  10. Siren 12V
  11. 12V DC power supply at more 1A. For example 12V battery or AC adapter.
  12. Universal PCB and more parts
Not only that I have an old circuit like this but use the infrared principle.

Infrared Intruder Alarm circuit diagram

This is an Infrared Intruder Alarm circuit that interesting. Imagine some people walk through restricted areas. At that moment, this circuit immediately sounded to alert you. It uses the principle of cut the infrared light. The circuit will recognize, control relay runs and turns on a warning signal like a siren for us to hear. This circuit is suitable for learning the infrared operation. Or, we can apply other controls Because using a relay. It uses the general parts you can buy easily in a local store near your house. Sound good, doesn’t it? Want to know how?

How it works

Look at in the circuit below.
infrared intruder alarm circuit
This circuit consists of 2 major parts, transmitter and receiver.


It is an Infrared signal transmission sector. Use a few parts. Look: an infrared LED is a special LED. When we power to it. We cannot see light. But can use it. It will emit the infrared light. If uses a pulsating DC voltage. It can spread the light radius better than stable DC. Use The 555 timer and others produce a varying DC voltage. It is a square waveform high-frequency output, 5kHz. And using power transistor- TIP42 to crease a current up to the infrared LED. May have a radius of up to 15 meters.


Let’s see the infrared receiver section at below of the circuit. We use a photodiode to receive the infrared light. Or use the phototransistor or the infrared module. Which is better? I think the last one is the best. Because it is so easy. The module has preamplifier inside. However, this circuit uses just photodiode (it is an old circuit). So, we need to use a preamplifier to increase a signal from photodiode. Then, transform it into DC voltage by D1, D2, R8, and C. This signal is still weak. We need to boost up to higher by 741 op-amps or CA3130. And enough signal comes out of pin 6. But Q3 does not work. Because it is a PNP transistor. So, the relay does not work too. Not only that, After that, we try to conceal the infrared beam. So, No output signal to a base of Q3. But It is a biased base of PNP transistor. With this why Q1 drive relay pulls in contact to turn on a siren or your load runs. This circuit uses a 9V power supply as a power source. Should use a DC regulator to limit any noise.

Parts you will need

All Resistors 0.25W, Tolerance 5% Transmitter IC1: NE555 Timer R:22K R:2.7K R:330 ohms Q-TIP42, PNP Transistor C: 0.01uF 50V Ceramic capacitor Infrared LED Receiver Q1,Q2 BC109 NPN transistors Q3: BC327 PNP transistor IC: CA3130 RY1: 9V 1 Contact Rely Electrolytic Capacitors C1: 470uF 16V C5: 1uF 50V Ceramic Capacitors C2: 0.01uF 50V C3, C8: 56pF 50V C4: 0.22uF 50V C6: 0.022uF 50V C7: 0.47uF 50V C9: 0.1uF 50V D1, D2: OA91 Diodes D3: 1N4002 Diodes R1, R7: 220K R2: 220 ohms R3: 2.2K R4: 560K R6: 2.7K R8: 47K R9: 10K Photodidoes


Note: This circuit is gradually incomplete. So, you need to sure to make it. However, It is a good teacher for who love to learn Electronics.

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I always try to make Electronics Learning Easy.

This Post Has 25 Comments

  1. PIR Sensor required for inst/test/comm at west bengal.Kindly send your tech detailed with price offer for approx 100 nos.


  2. hye i’m want to use this for my school project and i was wondering if you could explain to me further about the circuit. can i change the siren to maybe a lamp? and what id the use of the LED?

  3. Remove relay and put pilot lamp 9v to replace. For led series with resisitor 330 ohm 1/4w with one led

  4. hi, this is for my project.. may i replace the siren into LED? are the schematic still the same?
    i need to the the operation of the circuit…

  5. I want to use this ckt but not response properly.what is the code of motion pir sensor?

  6. when i try this circuit…relay still not function..i try check the voltage across is 2++ volt..what happened.?

  7. LED polarity is reversed

  8. how can we increase time delay

  9. i am using this circuit for my project. i have used a 12v o/e/n 57dp relay. the components are in good working condition. but when connected to circuit… its not working…

    please help me..

  10. Relay is not working

  11. Me too also commented on january 15 2015…. that the circuit is not working…
    but its working now after a few modification..

    I have made this circuit successfully for my 4th semester mini project..

    Please note the following to make it working..

    1. Do not use the capacitor C1… as it delays the relay to activate

    2. Use a 6v relay for better performance

    3. Also the led is connect wrong… reverse the connection of the led…

    4. It is better if we use a 12v 1A rectifier for input voltage

    1. can you send circuit design..please

    2. Hello Bro, Could you please send me this Circuit design

  12. I have made this circuit successfully for my 4th semester mini project..

    Please note the following to make it working..

    1. Do not use the capacitor C1… as it delays the relay to activate

    2. Use a 6v relay for better performance

    3. Also the led is connect wrong… reverse the connection of the led…

    4. It is better if we use a 12v 1A rectifier for input voltage

    1. Could you please send me the full Circuit design

  13. Hello,
    Thank you so much for good circuit. I have also made this circuit
    successfully . But the led connection has wrong way .if give it up the positive side of led with motion sensor output line and give it other side of led with ground. so it will be succeed.
    thank you

  14. Hi, what is the voltage to give for pir motion sensor

  15. This site is very good to know electronic user

  16. Problem is if we remove the capacitor circuit wont be able to hold the alarm for 20 seconds
    So this sucks ! 20 sec for start and 20 sec for end ?

  17. Hi!
    May i know what was the specific function of the transistor and diodes in the ckt above? please help advise.

  18. does this sensor detects something present in how long distance?

  19. what sort of things can this be able to detect and how does detection range changes according to obstacle?

  20. Can you give design of this circuit for all components…pls

  21. pls help me for design the circuit

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