When the 49 Ohm resistor opens and the zener smokes, you get 12 volts on the Arduino. Short any of the components in the schematic and you will not get 12 volts.
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A Schottky (clamping) diode between Arduino pin and VCC and 10k resistor could be a better option.
Don't forget that max pin voltage is not 3.3volt, but "VCC+0.5volt".
Leo..
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