Reversing radar: ultrasonic, buzzer and I2C LCD, on an Arduino Uno

// A reversing radar: the closer the wall, the faster the beeps.
//
//   HC-SR04 VCC -> 5V   TRIG -> pin 8   ECHO -> pin 7   GND -> GND
//   active buzzer + -> pin 9, - -> GND
//   I2C LCD GND -> GND   VCC -> 5V   SDA -> A4   SCL -> A5
//
// The beep is timed with millis(), not delay(), so the sensor keeps being
// read between beeps: under 5 cm it beeps every 0.1 s, under 10 cm every
// 0.5 s, under 20 cm every second, and further away every two seconds.
//
// Drag the distance slider on the sensor.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const int TRIG = 8;
const int ECHO = 7;
const int BUZZER = 9;

LiquidCrystal_I2C lcd(0x27, 16, 2);
unsigned long lastBeep = 0;

long distanceCm() {
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  long echo = pulseIn(ECHO, HIGH, 30000UL);
  return echo / 58;
}

unsigned long intervalFor(long cm) {
  if (cm > 0 && cm < 5) return 100;
  if (cm > 0 && cm < 10) return 500;
  if (cm > 0 && cm < 20) return 1000;
  return 2000;
}

void setup() {
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  pinMode(BUZZER, OUTPUT);
  lcd.init();
  lcd.backlight();
  lcd.print("Reverse radar");
  Serial.begin(9600);
  Serial.println("Mokxi Uno: reversing radar, sensor on 8 and 7, buzzer on 9");
}

void loop() {
  long cm = distanceCm();
  if (millis() - lastBeep >= intervalFor(cm)) {
    lastBeep = millis();
    digitalWrite(BUZZER, HIGH);
    delay(50);
    digitalWrite(BUZZER, LOW);
  }
  lcd.setCursor(0, 1);
  lcd.print("Dist: ");
  lcd.print(cm);
  lcd.print(" cm     ");
  delay(50);
}