Geolocation: How Wi-Fi and Bluetooth devices track you
Geolocation is not only done by using mobile antennas triangulation. It is also done using the Wi-Fi and Bluetooth devices around you. Operating systems makers like Google (Android) and Apple (IOS) maintain a convenient database of most Wi-Fi access points, Bluetooth devices, and their location. When your Android smartphone or iPhone is on (and not in Plane mode), it will scan actively (unless you specifically disable this feature in the settings) Wi-Fi access points, and Bluetooth devices around you and will be able to geolocate you with more precision than when using a GPS.
This active and continuous probing can then be sent back to Google/Apple/Microsoft as part of their Telemetry. The issue is that this probing is unique and can be used to uniquely identify a user and track such user. Shops, for example, can use this technique to fingerprint customers including when they return, where they go in the shop and how long they stay at a particular place. There are several papers and articles describing this issue in depth.
This allows them to provide accurate locations even when GPS is off, but it also allows them to keep a convenient record of all Wi-Fi Bluetooth devices all over the world. Which can then be accessed by them or third parties for tracking.
Note: If you have an Android smartphone, Google probably knows where it is no matter what you do. You cannot really trust the settings. The whole operating system is built by a company that wants your data. Remember that if it is free then you are the product.
But that is not what all those Wi-Fi access points can do. Recently developed techs could even allow someone to track your movements accurately just based on radio interferences. What this means is that it is possible to track your movement inside a room/building based on the radio signals passing through. This might seem like a tinfoil hat conspiracy theory claim but here are the references with demonstrations showing this tech in action: http://rfpose.csail.mit.edu/ [Archive.org] and the video here: https://www.youtube.com/watch?v=HgDdaMy8KNE [Invidious]
Other researchers have found a way to count the people in a defined space using only Wi-Fi, see https://www.news.ucsb.edu/2021/020392/dont-fidget-wifi-will-count-you [Archive.org]
You could therefore imagine many use cases for such technologies like recording who enters specific buildings/offices (hotels, hospitals, or embassies for instance) and then discover who meets who and thereby tracking them from outside. Even if they have no smartphone on them.
Again, such an issue could only be mitigated by being in a room/building that would act as a Faraday cage.
There is not much you can do about these. Besides being non-identifiable in the first place.
Source: The Hitchhiker’s Guide to Online Anonymity, written by AnonyPla © CC BY-NC 4.0