An electrochromic rearview mirror is installed on higher end vehicles. It consists of two lenses that sandwich an electrochromic (electronic color changing) gel. This gel, when charged with electricity, darkens. The mirror uses a forward sensor which measures the outside ambient light, and a rearward sensor to look for glare. When dark enough, it sends current to the electrostatic gel, darkening it a rate which is related to the level of ambient darkness and rearward glare. When the outside ambient light increases, the current decreases, until the gel is clear again at daylight light levels. The inside sides of the lenses are coated with a transparent, conductive layer, and the deepest lens has a reflective (mirror) coating. There is no tab to pivot the mirror. For more info, see: www.gentex.com/auto_how_nvs_work.html.