There are three types of range finders for golf. The cheap ones are exactly what c3shooter described. Then there are GPS models that are based on the layout of the course and your GPS location. The third kind, which I have, is exactly the same as a hunting laser range finder. It uses a laser that bounces off a target. It's also priced the same. Mine says Callaway on it but its made by Nikon. The most popular models are made by Bushnell.
On a side note, the cheap ones that work optically are based on the same principle as mil-dots.