  The number of mobile devices, such as smartphones and smartwatches, is
relentlessly increasing to almost 6.8 billion by 2022, and along with it, the
amount of personal and sensitive data captured by them. This survey overviews
the state of the art of what personal and sensitive user attributes can be
extracted from mobile device sensors, emphasising critical aspects such as
demographics, health and body features, activity and behaviour recognition,
etc. In addition, we review popular metrics in the literature to quantify the
degree of privacy, and discuss powerful privacy methods to protect the
sensitive data while preserving data utility for analysis. Finally, open
research questions a represented for further advancements in the field.
