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 to show simple circuits. You can do easy. This circuit is a piece of cake for you.

Motion detector alarm circuit with PIR sensor

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. 

See the circuit diagram below.

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 louder.

At 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 to use the delay time of the siren alert for 20 seconds.

For 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 protects a discharge voltage of C1, not reverse to PIR sensor.

Also, in a signal of the output of the PIR sensor is AC form with negative voltage.

So, the diode rectifiers 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 an expensive little.

We should use a good power supply at 12V. Although, the module has a regulated supply inside. But someones may not have it. The battery 12V is a good choice.

What is a PIR sensor?

See below!

Infrared PIR Human Motion Sensor Detector Modules

Cr: Image by Gowoops

Some called the Human Detector module. The 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.

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. R2: 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 infrared operations. Or, we can apply other controls Because of 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 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 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 below of the circuit.

We use a photodiode to receive 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 a preamplifier inside.

However, this circuit uses just a photodiode (it is an old circuit). So, we need to use a preamplifier to increase a signal from the 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 the 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%

IC1: NE555 Timer
R:330 ohms
Q-TIP42, PNP Transistor
C: 0.01uF 50V Ceramic capacitor Infrared LED


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 those who love to learn Electronics.

Get Ebook: Simple Electronics Vol-03


I always try to make Electronics Learning Easy.

28 thoughts on “Motion detector alarm circuit with PIR sensor”

  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. 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…

  4. 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..

  5. 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

  6. 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

  7. 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

  8. 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 ?

    • Hello Julius,
      Thanks for your visit. I am happy you are interested in this circuit.

      See in text again.
      R1: 1.2K to 2.2K, 0.25W Resistor
      R2: 1K, 0.25W Resistor



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