unsigned long mytime; 
byte led=13;
byte pir1=7;

void setup() {
 pinMode(led, OUTPUT);
 pinMode(pir1, INPUT);

}

void loop() {
  millis()-mytime >100 ;{
    mytime=millis();
   if(digitalRead(pir1)==HIGH){
    digitalWrite(led, HIGH);
   }
  }

}