int sensor = 2;
int state = LOW;
int val = 0;

void setup() {
  pinMode(sensor, INPUT);// put your setup code here, to run once:
  Serial.begin(9600);
}

void loop() {
  val = digitalRead(sensor);// put your main code here, to run repeatedly:
  if (val == HIGH){

    if(state == LOW) {
      Serial.println("Motion detected!");
      state = HIGH;
    }
  }
  else {
    if(state == HIGH){
      Serial.println("Motion stopped!");
      state = LOW;
    }
  }
}