const int pirPin=15;
const int ledPin=12;
bool flag=false;
void setup() {
  // put your setup code here, to run once:
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  attachInterrupt(pirPin, PIR_Detect, CHANGE);
}

void loop() {
  // put your main code here, to run repeatedly:
  if (flag) {
  digitalWrite(ledPin, HIGH);
  }else{
    digitalWrite(ledPin, LOW);
  }
}
void PIR_Detect(){
  flag=!flag;
}