I got nabbed by one of these scanners in Chisinau. I didn't hear a beep or anything but the guy told me to come to the side for additional screening. They scanned by bags and asked me about laptops. They told me that I had to pay an import tax on one laptop as only a single laptop is allowed duty free. I showed them the laptops and showed them that one had my company sticker on it and the other was several years old. They finally let me pass. I guess people go abroad and buy laptops for cheap and bring them here without paying the tax.

Never seen these scanners in the US and I'm not even sure how they choose to screen passengers there.