int pir_1 = 2;
int pir_1_state = LOW;
int pir_2 = 3;
int pir_2_state = LOW;
int relay_1 = 4;
int relay_1_state = 0;

void setup() {
  pinMode(pir_1, INPUT);
  pinMode(pir_2, INPUT);
  pinMode(relay_1, OUTPUT);
  attachInterrupt(digitalPinToInterrupt(pir_1), enable_relay_1, CHANGE);
  attachInterrupt(digitalPinToInterrupt(pir_2), enable_relay_2, CHANGE);
}

void loop() {
}

void enable_relay_1 () {
  pir_1_state = digitalRead(pir_1);
  if (pir_1_state == HIGH) {
    digitalWrite(relay_1, HIGH);
  }
  else {
    digitalWrite(relay_1, LOW);
  }
}

void enable_relay_2 () {
  pir_2_state = digitalRead(pir_2);
  if (pir_2_state == HIGH) {
    digitalWrite(relay_1, HIGH);
  }
  else {
    digitalWrite(relay_1, LOW);
  }
}