There's this parking garage I use, which lets you scan your ticket and pay on your phone. At the end, it gives you a barcode for the scanner to scan. All's good. One day, I hadn''t managed to get my phone out the window to let it get scanned before the arm opened. Weird, must be a pretty good scanner. That happened another time or two, pretty convenient, nobody likes to have to stretch way out of their car to scan a barcode. The next week, I pulled up and before taking my phone off the mount, I turned back to tell my kid something, and...the arm opened. Wow, that's a great scanner. The week after that, I decided to hold my phone in such a way that it couldn't be seen, and slowly lifted it up, but before my phone was visible to the scanner, the arm opened. Another week, another barcode. This time, I left my phone on the mount. The arm opened. Yet another week, I turned my phone away from the scanner before getting to the gate. I pull up and the arm opened. Finally it hit me. I made it so that the scanner couldn't possibly see my phone. The arm opened. My best guess is that when you visit the website, it grabs your Bluetooth mac address and when you get to the gate, it sees that address and opens the arm. I just checked the site and there are no Bluetooth permissions. I guess you don't need anything special for that? As with many things, you lose a bit of privacy for a bit of convenience. I don't know if I can even opt out of this (as per custom).