That was what I was thinking of. I was just assuming it was IR. I have heard that they look at utility bills also. Our local builing dept goes to Home Depot once a month to look for reciepts over 500.00. If over that then they look for permits being issued.
I don't doubt that of course I am a scoflaw, I had 19 yards of concrete for a new slab for my shop, had it poured on the weekend, come monday what are they gonna do make me tear it up? I don,t think so.