int ledPin = 13;                // choose the pin for the LED
int inputPin = 4;               // choose the input pin (for PIR sensor)
boolean pirState = LOW;             // we start, assuming no motion detected
int val = 0;                    // variable for reading the pin status

void read_PIR();

void setup() 
{
  pinMode(ledPin, OUTPUT);      // declare LED as output
  pinMode(inputPin, INPUT);     // declare sensor as input

  digitalWrite(ledPin,LOW);

  Serial.begin(9600);
}

void loop()
{
  read_PIR();
}

void read_PIR()
{
  val = digitalRead(inputPin);  // read input value of PIR sensor
  if (val == HIGH)
  { 
    digitalWrite(ledPin, HIGH); 
    if (pirState == LOW) 
    {
      Serial.println("Motion detected!");
      pirState = HIGH;
    }
  } 
  else 
  {
    digitalWrite(ledPin, LOW); // turn LED OFF
    if (pirState == HIGH) 
    {  
      Serial.println("Motion ended!");
      pirState = LOW;
    }
  }
}