I was having trouble with the sensor showing an open status. It always showed closed. But it showed active when the door was moving. I mounted it as instructed in the lower right corner. The garage door has four panels. I finally noticed that when the door is open the bottom panel with the sensor is not all the way up and parallel to the ground. It stays at a slight angle. I moved the sensor up one panel and it works fine now. With it mounted there it makes a full 90 degree movement.
Not sure if anyone else had this problem, but a note in the instructions about making sure the sensor travels a full 90 degrees might help.