Dynamic Laser Tripwire/Alarm

const int threshold = 920;
const int Laser = 9;
const int Led/Buzzer = 12;
bool Alarm = false;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(Laser, OUTPUT);
  digitalWrite(Laser, HIGH);
}

void loop() {
  // put your main code here, to run repeatedly:
  int Value = analogRead(A0);
  Serial.println(Value);
  if(Value < 800){
    tone(12, 4000);
  }else if(Value > 800){
    noTone(12);
  }
 
  
}