Not sure this is a repost, however, it is interesting to watch. Many people have stated and believe that you have to be straight on with laser for a detector to pick it up. This is not 100% true, light bounces around especially non visible light, some surfaces will reflect infrared light as you can see in this video. Also infrared can pass through some materials as well.
[ame=http://www.youtube.com/watch?v=N-oOCDgePMY]YouTube - Valentine V1 Laser Sensitivity Test[/ame]