Just last night, I was on a forced shopping spree in my favorite supermarket and, in a leisurely moment, decided to look up past the glare of the suspended lighting system. There are all kinds of electronic systems. The refrigerated cases have temperature monitors, and I believe even have proximity sensors that monitor physical presence in the aisles. Their inventory policy is rather lax, because they have a habit of leaving their inventory devices on top of these tall cases. When we get to the self checkout point we use a shopper's id card for "valued customers". You can bet they have a database compiled with everything in there but our shoe sizes.