int state= LOW; //LOW or 0 ===> Flag

void setup()
{
  pinMode(9,OUTPUT);
  pinMode(3, INPUT);
  Serial.begin(115200);
}

void loop() 
{
  if (digitalRead(3)==HIGH)
  {
    digitalWrite(9, HIGH);
    if (state == LOW)
    {
      Serial.println("Motion Detected!");
      state = HIGH;
    }
  }
  else
  {
    digitalWrite(9,LOW); 
    if (state == HIGH)
    {
      Serial.println("Motion Ended!");
      state = LOW;
    }
  }
}