Making a motion sensor alarm with an Arduino is a great electronics project for beginners. With just a few basic components, I can build an alarm that will detect movement and sound an alarm. This project is simple enough for beginners but also teaches some core concepts that can be built upon for more advanced projects.

What You Will Need

To build this motion sensor alarm, you will need:

I recommend getting an Arduino starter kit that includes many of these parts to get started. You will also need the Arduino IDE installed on your computer.

How a PIR Motion Sensor Works

The key component that makes this project work is the passive infrared (PIR) motion sensor. This simple sensor detects infrared radiation that is given off by warm bodies passing within its range.

Inside the PIR sensor are two slots that detect infrared. The slots are somewhat offset so that an infrared source passing by will trigger one slot slightly before the other. This delay causes a voltage difference that is detected by the sensor circuitry.

When motion is detected, the PIR sensor will output a short high pulse signaling that motion was found. We can detect this pulse in our Arduino code to sound the alarm.

Circuit Diagram

The circuit for this motion sensor alarm is very simple:

Here is a circuit diagram showing the connections:

How to Make a Simple Yet Effective Motion Sensor Alarm with an Arduino and Basic Electronic Components

Arduino Code to Detect Motion and Sound Alarm

With the circuit assembled, the Arduino code will detect motion and activate the alarm.

The code does the following:

Here is the full Arduino code:

// Motion Sensor Alarm

int pirPin = 3; // PIR Out pin
int buzzer = 9; // Buzzer pin

void setup() {

pinMode(pirPin, INPUT);
pinMode(buzzer, OUTPUT);


void loop() {

if (digitalRead(pirPin) == HIGH) {

digitalWrite(buzzer, HIGH); 
digitalWrite(buzzer, LOW);



This code is very simple but effective. Whenever motion is detected, it will sound the alarm for one second before resetting.

Putting it All Together

Follow these steps to build the motion sensor alarm with your components:

  1. Build the circuit as shown in the diagram above on your breadboard.
  2. Upload the Arduino sketch to your board.
  3. Open the Arduino serial monitor and ensure the code is running.
  4. Power your Arduino board with a 9V battery or USB supply.
  5. Wave your hand in front of the PIR sensor. The buzzer should sound for 1 second when motion is detected.
  6. Adjust the PIR sensor potentiometer as needed to change sensitivity.
  7. Optionally enclose your project in a box or casing for a self-contained alarm.

And that's it! With just a simple Arduino circuit, we can detect motion and sound an alarm. This is a great starter project to learn the basics of Arduino, sensors, and alarm systems.

Some ways you could expand this project further:

The possibilities are endless! With the core concepts from this project you'll be able to create much more advanced motion sensing projects.

Let me know in the comments if you have any questions about building your own motion sensing alarm with Arduino!