  Physical retailers, who once led the way in tracking with loyalty cards and
`reverse appends', now lag behind online competitors. Yet we might be seeing
these tables turn, as many increasingly deploy technologies ranging from simple
sensors to advanced emotion detection systems, even enabling them to tailor
prices and shopping experiences on a per-customer basis. Here, we examine these
in-store tracking technologies in the retail context, and evaluate them from
both technical and regulatory standpoints. We first introduce the relevant
technologies in context, before considering privacy impacts, the current
remedies individuals might seek through technology and the law, and those
remedies' limitations. To illustrate challenging tensions in this space we
consider the feasibility of technical and legal approaches to both a) the
recent `Go' store concept from Amazon which requires fine-grained, multi-modal
tracking to function as a shop, and b) current challenges in opting in or out
of increasingly pervasive passive Wi-Fi tracking. The `Go' store presents
significant challenges with its legality in Europe significantly unclear and
unilateral, technical measures to avoid biometric tracking likely ineffective.
In the case of MAC addresses, we see a difficult-to-reconcile clash between
privacy-as-confidentiality and privacy-as-control, and suggest a technical
framework which might help balance the two. Significant challenges exist when
seeking to balance personalisation with privacy, and researchers must work
together, including across the boundaries of preferred privacy definitions, to
come up with solutions that draw on both technology and the legal frameworks to
provide effective and proportionate protection. Retailers, simultaneously, must
ensure that their tracking is not just legal, but worthy of the trust of
concerned data subjects.
