Three-way switch with motion sensor
I have a three-way switch controlling lights in the front entry and stairs that lead from that area to the main home upstairs. These lights are controlled by a switch by the front door, and a switch at the top of the stairs. My bedroom is below and my kids' bedrooms above. When the wake up at night, I don't want them coming down the steps in the dark. So I wanted to add a motion-sensor at the top switch. When I opened this switch box, there were just three wires connecting the original switch. I hooked up the motion sensor switch, which can be for two or three-way. It works great EXCEPT that if I turn on the lights from below it now shorts the circuit. Is there a way to fix this, or do I need to disconnect the switch below or call an electrician? Thank you for any help!