Smart city models rely significantly on crowd and people surveillance, namely on systems collecting information about citizens’ location in near-real time using signal-based sensors or other techniques and processing this data to generate insights about the movement and behavior of people within a specific area in order to facilitate data-driven decision-making. While these data-gathering innovative applications can offer valuable insights for business management, the fact that they capture and process data in a seamless and often invisible way undermines the ability of individuals to effectively identify intrusive practices and associated privacy risks. Continuous tracking and analysis of individuals’ movements may result in the creation of behavior-based profiles, raising severe concerns about potential misuse, from targeted advertising and privacy violations to discrimination and security risks. This paper discusses, in light of the European privacy regulatory framework, the application of the transparency principle in the interconnected data ecosystem of smart cities, where various technologies, sensors, devices, and databases are integrated in order to collect, analyze and share data for urban management and improvement.