Those motion detectors are using infrared radiation as the sensing solution.
Unless you strap a live cat to the garage door, it will not sense it
opening. Some motion detectors use microwave technology and can actually be
tuned to "see" through walls and activate. Still, they will not detect the
door. Why don't you wire in a garage door switch to a fixture. When the door
is up, the relay closes and the light comes on. When the door is down, the
relay opens and the light goes off.
The door movement wont affect it, good sensors dont false trip. Mine is
pointed at the door it wont trip, but the car pulling in does