Auto-dimming Mirror (Electrochromic Mirror)

It is most common on the interior rear-view mirror. Some cars also have auto-dimming door mirrors, controlled by the interior mirror. One sensor measures ambient light ahead and another measures glare from behind. When reverse gear is selected, many cars switch the mirror back to full brightness to give a clear view.

When glare is detected, a voltage is applied to a gel layer between two glass panes, which darkens and absorbs part of the light.

A cracked electrochromic mirror can leak gel, which should not touch skin or paint. Objects hanging from the mirror or a dirty sensor can stop it working properly.