int irmotionPin = 4; 
int relayPin = 8;  

void setup(){
  Serial.begin(9600);
  pinMode(relayPin, OUTPUT);  
  digitalWrite(relayPin, LOW); 
}

void loop()
{
  while (digitalRead(irmotionPin) == HIGH) 
  {  
  digitalWrite(relayPin, HIGH); 
  Serial.println("Relay is ON");
  delay(500);
}

digitalWrite(relayPin, LOW);  
Serial.println("Relay is OFF");
delay(500);
}