The New York Times reports on how stores use bluetooth beacons to track your every move. A snippet (emphasis added):
In order to track you or trigger an action like a coupon or message to your phone, companies need you to install an app on your phone that will recognize the beacon in the store. Retailers (like Target and Walmart) that use Bluetooth beacons typically build tracking into their own apps. But retailers want to make sure most of their customers can be tracked — not just the ones that download their own particular app.
So a hidden industry of third-party location-marketing firms has proliferated in response. These companies take their beacon tracking code and bundle it into a toolkit developers can use.
The makers of many popular apps, such as those for news or weather updates, insert these toolkits into their apps. They might be paid by the beacon companies or receive other benefits, like detailed reports on their users.