Sensors question

OK ... some silly questions, but ...

On my '95 Outback L.L. Bean there are three sensors that help run the climate control system. The one I'm interested in is the knob-looking one on the dashboard on the passenger side.

What exactly does this sensor do and how does it do it? The reason I ask is because here in Massachusetts, the inspection sticker is placed on the lower left side of the window -- which may block this sensor. If the sensor detects heat, there's probably no problem, but if it detects light, I'm wondering if the placement of the inspection sticker would cause an issue. Even though the sticker is very thin, it casts a shadow on the sensor.

Does it matter?

Secondly, on the auto-dimming mirror, there is a photosensor on both the front and the back of the mirror. What does the one on the side facing the windshield collect? Glare from headlights hitting the windshield? I ask here because of the placement of a toll responder device which normally sits behind the mirror on the passenger side -- again I want to make sure this unit does not block the sensor such that it impedes it's effectiveness.

Silly questions, perhaps, but please let me know your thoughts.

Thanks.

cbbl