Bluetooth beacons are small devices that some stores hide throughout the building. Apps on your phone can pick up the signals they emit and send information back.
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.
I bet iOS 13’s new Bluetooth controls will affect this.