Distance meter

#include <Ultrasonic.h>       
#include <TM1637Display.h>   

byte RED=2; 
byte GREEN=3;
byte DIO=5; 
byte CLK=4;
byte BUZZER=6;
byte TRIG=7;
byte ECHO=8;

Ultrasonic ultrasonic(TRIG, ECHO);
TM1637Display display(CLK, DIO);

void setup() {
  pinMode(GREEN, OUTPUT);
  pinMode(RED, OUTPUT);
  pinMode(BUZZER, OUTPUT);

  display.setBrightness(90);   
  Serial.begin(9600);            
}

void loop() {
  int distance = ultrasonic.read();
  display.showNumberDec(distance);

  if ( distance < 30) {
    digitalWrite(GREEN, LOW);     
    digitalWrite(RED, HIGH);      
    digitalWrite(BUZZER, HIGH);   
    Serial.println("WARNING"); 
  } else {
    Serial.println("SAFE");
    digitalWrite(GREEN, HIGH);    
    digitalWrite(RED, LOW);       
    digitalWrite(BUZZER, LOW);    
  }

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  delay(200); 
}