Mercedes-Benz rear view mirror

Question

What does the little black circle at the top right of the interior rear view mirror do?

Answer 1

god i couldnt find that c**p in the manual

Answer 2

It's a sensor for the automatic-dimming (anit-dazzling) mirrors. At night it will sense how bright the headlights are on a trailing vehicle. A control module then sends a signal to the inside rearview mirror, and the driver's outside mirror. They will then dim the reflection, and the brighter the follwing lights the more dimming effect you get.

In the mirrors there is an emulsion spread between two layers of glass, and electrical current flows through the emulsion. When voltage of the current increases the emulsion becomes darker, dimming the reflected light.

Answer 3

It might be a light sensor for the mirror to automatically switch between day and night modes.