Our original sensor reliably gave "Open" and "Closed" data regarding our garage door until recently, when it would fail to signal "Closed" a significant number of times. I noticed that when this was the case, the lights on the sensor would fail to illuminate, leading me to believe the sensor was at fault.
I bought a new sensor to solve the problem, and for the most part it has. But there has been at least one instance when the sensor failed to signal "Closed" when it should have.