Share 'before infrared cameras ????'

Before we had our high tech tools, how did we know if there was insulation in the walls? What were the methods? How funny that I can use a camera but than can't figure out how was it done in the past without drilling holes on the wall and than you had to patch it? That doesn't seem like a cost effective way to bid a job. Or is it another rule of thumb? Like In So. Cal houses built before the 70's…