This is designed to sense whether or not my garage door is open. Since the door doesn't always stop at the same place when rolled up a magnetic sensor wouldn't work.

The friction between the sensor arm and the plastic pin causes by the microswitch roller sometimes keeps the arm from falling back down so I added a nut for weight that is held on by a small screw. This version includes a hole in the sensor arm for the screw.

You might need to clean up the hole through the sensor arm with a drill bit (depends on your printer). I printed with thick shells to allow for this.

Apply a little acetone to just the smallest diameter portion of the pin and insert through the arm into the plate. Try to avoid getting any acetone on the arm. You can work the arm back and forth as the acetone dries to make sure the arm doesn't stick.