Check if sliding door is closed

Hey guys!

I want to check if the sliding door of my terrarium is closed using the Puck.js (light green LED if it is closed, else light red LED). I found a cool tutorial, where I can see how to do this using a magnet.

But I think a better solution would be to attach 2 wires to the Puck.js and then put a metal plate on the side of the door. If the door is closed, the circuits is also closed and otherwise it's open.

I'm not very familiar with the Puck.js so far, so I have two questions for this idea:

1. To which pins should I connect the two wires?
   
2. How can I determine, if the two wires are connected or not?
   
   

Thanks for your help!