const int relayPin = 4;  // define the output for relay
const int pirPin = 7;    // define the input where the PIR sensor is connected
int pirState = LOW;      // starting state for the PIR detector
int var = 0;             

void setup() {
  pinMode(relayPin, OUTPUT);
  pinMode(pirPin, INPUT);
}

void loop() {
  pirState = digitalRead(pirPin);
  if(pirState == LOW){
     // nothing is moving; no change
     digitalWrite(relayPin, LOW);
  }
  else{
     digitalWrite(relayPin, HIGH);
  }
}