Works great in complete darkness! Just finished it.
http://www.digital-photo-secrets.com/tip/1303/how-to-use-trap-focus-to-get-better-sports-and-wildlife-shots
The hardest part is lining up the laser and 300mm lens, since you can't see it easily. Once that is done you just point and shoot in the dark. Either with a flash or tripod long exposure. It works reliably out to 100m and so does a high powered flash. Focusing is not so critical at that distance, but at 50m it is with large apertures. You can aim it straight down a trail in the woods in the dark, not across it. If anyone, or anything breaks the beam anywhere along the trail the camera immediately triggers after focusing. Don't worry it won't hurt your eyes at that distance, the beam is inches across at 50m. I can defocus it at close range at the expense of maximum distance. The Uno doesn't have much to do. It simply fires the laser and presses the button on the camera 1 out of 10 seconds. If you left it on it would overheat and empty the batteries. Already I have a 2" heatsink. The beam is invisible in the dark. Takes 1/4s to achieve focus.
What other way can you detect a moving person at 100m?
Any ideas what to do with this "sensor"?
Besides take pictures...