Setup: Two Switches for one light, one downstairs and one upstairs in a stairwell.
Old Switch Wiring (black is in common of switch)( same type of switch upstairs)
New Switch: Lutron Maestro Motion Sensor switch, 2-Amp, Single-Pole, White
So here is the interesting part
With upstairs switch down, black wire from wall to green of new switch causes the new switch to click/switch but no lights
If the switch upstairs is up then the earth grounding wire (to the new switches green wire) works(light turns on) (when upstairs switch is down it doesn't light up)
Edit: Updated some wording to make it more clear