Density.io
Risky. MAC address tracking is definitely a legal 'grey area' at the moment. I can imagine mining/fingerprinting in this way could easily become illegal in the not-to-distant future.<p>In the UK, City of London already banned the wifi-enabled bins that were tracking MAC addresses.<p>It would be really easy to tie a name to MAC address (from point of purchase with a credit card), then see exactly where that person went via the 'sharing' of data with other retailers. This is certainly something you would expect to need 'opt in' to.