[sjf]

Yes, visit tracking has been around for years. Here is one product (https://support.google.com/google-ads/answer/6100636?hl=en), I assume there are many more.

I guess it's not more well-known because it's not in the stores interests to publicize it.

[flowless]

Any idea how it works? The site is not very helpful in that manner.

[verify_sirrah]

Presumably using Bluetooth beacons.

https://en.wikipedia.org/wiki/Bluetooth_low_energy_beacon

[closeparen]

Probably the same way that Google Maps traffic or “this restaurant is busy now” indications work.