const int BTN_PIN = 13;
const int LED_PIN = 15;

bool pressed;
unsigned long button_time = 0;
unsigned long last_button_time = 0;

void doCriticalThing() {
  digitalWrite(LED_PIN, HIGH);
  delay(225);
  digitalWrite(LED_PIN, LOW);
  delay(225);
}

void IRAM_ATTR isr() {
  button_time = millis();
  if ((button_time - last_button_time) > 500) {
	  pressed = true;
  } 
  last_button_time = button_time;
}

void setup() {
  pinMode(LED_PIN, OUTPUT);
	pinMode(BTN_PIN, INPUT_PULLUP);
	attachInterrupt(BTN_PIN, isr, FALLING);
}

void loop() {
	if (pressed) {
    doCriticalThing();
		pressed = false;
	}
}