Thanks for the ideas! The hinge method worked best for me. Placed a metal hinge in top center of garage door, drilled two pilot holes, then attached with two screws. Used a few small washers because hinge screws were slightly longer than door width. Cleaned the garage door and attached the main sensor using the existing adhesive. The small portion of sensor attaches to the hinge with just the magnet.
It works great so far. When door goes up, gravity drops down the hinge to open the sensor and show the door open. When it closes, the hinge goes flat against the door and sensor indicates door is closed. Also used some thin stick on rubber backing cut to size of the hinge to help cushion the force when door closes, but it worked fine without that.
