A) The voltage level of the digital output signal from the Arduino UNO is either 5 V (HIGH) or 0 V (LOW).

// Define the digital pins for the PIR sensor and the buzzer
const int pirSensorPin = 2;  // PIR sensor connected to digital pin 2
const int buzzerPin = 3;     // Buzzer connected to digital pin 3

void setup() {
  // Initialize the PIR sensor pin as an INPUT
  pinMode(pirSensorPin, INPUT);
  // Initialize the buzzer pin as an OUTPUT
  pinMode(buzzerPin, OUTPUT);

  // Optional: Start serial communication for debugging
  // Serial.begin(9600);
  // Serial.println("Intruder Alert System Initialized");
}

void loop() {
  // Read the state of the PIR sensor
  // pirState will be HIGH (1) if motion is detected, LOW (0) otherwise
  int pirState = digitalRead(pirSensorPin);

  // Check if motion is detected
  if (pirState == HIGH) {
    // If motion is detected, turn the buzzer ON
    digitalWrite(buzzerPin, HIGH);
    // Optional: Print status to serial monitor
    // Serial.println("Motion Detected! Buzzer ON.");
  } else {
    // If no motion is detected, turn the buzzer OFF
    digitalWrite(buzzerPin, LOW);
    // Optional: Print status to serial monitor
    // Serial.println("No Motion. Buzzer OFF.");
  }

  // A small delay can be added to prevent rapid toggling or to debounce the sensor
  // delay(50);
}