"Shopping center landloard DDR Corp. announced the launch of ValuText, a location-based, mobile marketing service designed to drive sales at 27 of its open air shopping centers.
Powered by Placecast, ValuText will send immediate offers from retailers within a designated shopping center via text message to opted-in shoppers once they enter a geo-fence around DDR's locations." - from here.
It is a "traditional" way - geo-fence. But you can do that with SpotEx. Wi-Fi network at retailer's location could be used as a trigger that shown new (hot etc.) items for customers nearby. Btw, customers do not need to discover their phones to retailer in this case.