int red = 2;
int green = 3;
int trig = 12;
int echo = 13;
int alarm = 10;

#define pitch 300

double duration, distance;

void setup()
{
  pinMode(red, OUTPUT);
  pinMode(green, OUTPUT);
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(alarm, OUTPUT);
}

void loop()
{
  digitalWrite(trig, LOW);
  delayMicroseconds(2);
  digitalWrite(trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig, LOW);
  delayMicroseconds(2);
  duration = pulseIn(echo, HIGH);
  distance = (duration / 2) * 0.0343;

  if (distance < 20)
  {
    digitalWrite(red, HIGH);
    digitalWrite(green, LOW);
    tone(alarm, pitch);
    delay(600);
    
    digitalWrite(red, LOW);
    digitalWrite(green, LOW);
    noTone(alarm);
    delay(600);
  }
  else
  {
    digitalWrite(red, LOW);
    digitalWrite(green, HIGH);
    noTone(alarm);
  }
}