Several miles underneath Brazil’s largest city, Sao Paulo, platform doors fitted with sensors have been installed across the city’s metro stations. These sensors judge each commuter’s reaction to the advertising displayed. These are then classified into four categories: happy, unsatisfied, surprised or neutral.

Harnessing facial recognition technology in this way enables advertisers to understand consumer reactions in context and in real time: creating an invaluable opportunity to truly understand ad effectiveness.

But before we get too excited, there are some limitations. Firstly, the technology onlygenerates surface level understanding; we can’t explore why a consumer has had a particular reaction to the advert. Furthermore, with consumer privacy coming under increasing scrutiny in light of the Facebook privacy scandal and the EU’s General Data Protection Regulation, there are concerns as to how receptive consumers will be to the technology being used in this way.