It's a replacement for your rear view mirror which automatically detects when it's dark and electronically dims the headlights from cars behind you. No moving parts like the first generation of these. The mirror turns slightly darker but you can still read the front tags on cars behind you but the headlights have no glare at all. The one I bought for the Miata also had a built-in outside temperature display (which the Volvo has already) and compass headings. Mine was a Mazda part but it was made by Donnelly. Visit their web site for more information http://www.donnelly.com. Donnelly is just of several suppliers for these.