http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7045210
https://www.element14.com/community/community/raspberry-pi/raspberrypi_projects/blog/2015/06/02/a-raspberry-pi-laser-tripwire-dog-watcher
http://www.dreamgreenhouse.com/projects/2013/picar/index.php One of those should help you...
Ill need something like this to record my "stunt"