Uhhh that exact technology has been in use for years. Your phone broadcasts/receivers a beacon at regular intervals while Bluetooth is on. Anyone can pick it up if they are looking.
https://www.nytimes.com/interactive/2019/06/14/opinion/bluetooth-wireless-tracking-privacy.html
The process is so streamlined companies bragged your advertising profile is updated before you check out.
The user may not be aware they have this tracking technology on their phone. The toolkit may be some app developer integrating a 3rd party library for analytics. Banking apps, loyalty apps, phone companies, games, utilities… they all can rely on 3rd parties for proximity services.
In fact, I was going to mention an app, Exodus, that can reveal these trackers and in scanning my phone, I found 2!. The first is home assistant, which is understandable, but the second is a Health app my doctor office uses! Man, that irks me!