I worked on that project (Shopping Buddy) and a few later iterations of it. This was before the iPad, we had these huge IBM super rugged tablets on the carriag

I worked on that project (Shopping Buddy) and a few later iterations of it. This was before the iPad, we had these huge IBM super rugged tablets on the carriages. We used something like Zigbee to triangulate the precise location of the carriage in the aisle, so we could tell whether the cart was at the beginning, middle or end of aisle 5 or aisle 6 and target ads appropriate for where you were. There was a small scanner for you to scan your groceries as you went. It was ridiculously expensive to outfit one store w/the tech so we ended up with a simpler version using Motorola MC70 handheld scanner guns and ditched the exact triangulation and instead went to more generic stuff where we would just check which AP you were connected to so we would know which third of the store you were on (produce, frozen foods, or middle of the store). That system then got ported to iOS and Android so you could use your phone instead of the scanner. The original version despite its issues was pretty advanced for the time (mid 2000s). They still have the mobile / MC70 version rolled out to the entire chain now, it's very successful from what I hear.