How To Build A Motion Sensor

Been reading tons of sites and watching strange tutorials on how to build a motion sensor. BUT this one really got my attention: http://antiadvertisingagency.com/wp-content/pdfs/how-to-article.pdf Oh Hey…Say WHAT 20th century?!?! A CD player!! *smh* Can you even find one of those outside of the 90’s ?!? Didn’t think so…