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Londoners Tracked By Advertising Firm's Trash Cans
schwit1 asks "How can I automatically have my wi-fi turn off when I leave the house unless I specifically turn it back on?" and provides this excerpt from Wired to illustrate why that would be useful: "Hundreds of thousands of pedestrians walking past 12 locations unknowingly had the unique MAC address of their smartphones recorded by Renew London. Data including the "movement, type, direction, and speed of unique devices" was recorded from smartphones that had their Wi-Fi on. First reported by Quartz, the data gathering appears to be a Minority Report-esque proof-of-concept project, demonstrating the possibility for targeted personal advertising. 'It provides an unparalleled insight into the past behavior of unique devices — entry/exit points, dwell times, places of work, places of interest, and affinity to other devices — and should provide a compelling reach data base for predictive analytics (likely places to eat, drink, personal habits etc.),' reads a blog post on the company's site. In tests running between 21-24 May and 2-9 June, over 4 million events were captured, with over 530,000 unique devices captured. Further testing is taking place at sites including Liverpool Street Station." (The name sounds a bit like a government project, but Renew London is actually an advertising / marketing firm.)
The 802.11 protocol does not require cell phones to broadcast their MAC addresses. Phones do it so that they can discover nearby networks faster, but it is completely optional.
Except, of course, that it does. In order to associate to an access point, you have to send your MAC address. [...]
To discover a nearby access point 802.11 only requires that you listen for the broadcast.
To connect to it, yes, you need to exchange MAC addresses - but this is only required if you actually want to connect to the AP.
The GP is correct, actively throwing your MAC address around to networks you have no desire to connect to is not required by the protocol and should be disabled by default.
Now, if your phone wants to go whoring around with every open AP just to save on wireless data transfer, that's a different problem...
Probably also something that should be disabled by default.