Data have become a central pillar of society. Technological advances in computational power, storage and network platforms have enabled the production, processing, analysis and storage of large volumes of digital data. Information that previously could not be stored, or captured can now be digitally recorded. Digital data have become a key asset for government, businesses and individuals supporting their decision making processes and shaping human behaviour. A notable example has been the use of digital data to monitor the COVID-19 pandemic and inform the development of appropriate interventions. A key data stream has been location data from mobile phones. These data have enabled monitoring the geographic spread of COVID-19 in near-real time with technological companies, such as Apple and Google releasing regular mobility reports. More generally, mobile phone data are a rich source of information offering a unique opportunity to capture human behaviour at an unprecedented geographic and temporal resolution. Yet, key challenges remain, such as issues about privacy, representativeness, biases and the use of large, noisy and complex data sets.