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Just in case anyone ends up here 4 years later:
Just wire the button with one wire to +12VDC(or +24dc) and the other wire to the input, such as A0. It will be low when the button is open, and high when the button is closed.
It only seems to support pulldown, or active high buttons unless you want to mess with an external resistor. This is not the common way to wire a button to an Arduino, but it seems to work great!