#include <Wire.h>

void setup() {

  Wire.begin(8);                // join i2c bus with address #8
  Wire.onRequest(requestEvent); // register event
  pinMode(8, INPUT);  // set button as input at pin 5
  Serial.begin(9600);  // start serial for output
}

void loop() {
  delay(100);
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()

void requestEvent() {

  if (digitalRead(8)) {
    Wire.write("0");
  }

  else {
    Wire.write("1");
  }
}