Doorbell: button on pin 2, buzzer on pin 8, on an Arduino Uno

// A doorbell: press the button and the buzzer plays ding-dong.
//
//   one side of the button -> 5V, the other -> pin 2 and 10k to GND
//   buzzer + -> pin 8, buzzer - -> GND
//
// The button reads HIGH while it is pressed, thanks to the 10k pull-down.
// tone() swings pin 8 at a frequency, and the buzzer turns that into a note:
// a high one, then a lower one.

const int BUTTON = 2;
const int BUZZER = 8;

void setup() {
  pinMode(BUTTON, INPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: doorbell. Press the button on pin 2.");
}

void loop() {
  if (digitalRead(BUTTON) == HIGH) {
    Serial.println("ding");
    tone(BUZZER, 659, 300);
    delay(350);
    Serial.println("dong");
    tone(BUZZER, 523, 500);
    delay(800);
  }
}