Here is a photo of a Velodyne LIDAR sensor. It uses lasers to make 3D scans of the surrounding environment.
Velodyne is a company better known for sub-woofers. They participated in the 2005 DARPA Grand Challenge for autonomous vehicles. The notable feature of their entry was the new LIDAR sensor that they had designed and built. My understanding is that the founders are quite the tinkerers and inventors and just decided to build a new LIDAR.
Many of the other teams were quite impressed with its performance and wanted to get one for themselves. The current version has 64 lasers that scan as the entire unit rotates. You can visit Velodyne's LIDAR page for more information. It's being used by several teams in the upcoming DARPA Urban Grad Challenge, including the Stanford team.
