I have used Nikon and Bushnell rangefinders for years while hunting in Colorado, it's amazing how you can misjudge the distance across a valley. I don't think they project a "beam" onto the subject but I may be wrong. I also don't know what the minimum distance is, which could come into play if close measurements are needed.
I think you have a good idea here, maybe you should market it! (I will need 10% of your gross sales for the idea