coincidence, shopping apps from companies like macy's and urban outfitters use the phone's gps to access your location. >> they have technologies that can follow you as you walk through sectors of the store and connect to your data so they know who you are. >> reporter: sure enough, after i installed the urban outfitters app it pings me as i walk into a store in philadelphia. in san francisco, it was almost a block away when the app lit my phone up with notifications. it makes sense, their best chance to get me into the store is when i'm close by. the macy's notifications were even more interesting. they pinged me once when i entered their store in philadelphia. i just put my hand on the door handle and a notification popped up saying welcome to macy's. they know i'm here. then again in san francisco two timely notifications, not in a macy's store but get this, while i was in other stores. they sent me a 30% off notification while i was in this store, one of their...