Sarkozy using geolocation for door-to-door campaigning (Knockin)
During the primary elections in November 2016, the former French president, Nicolas Sarkozy, reportedly used an app, called Knockin, that made it possible to identify and geolocate supporters for door-to-door campaigning. Based on a report by the French Radio RMC, the app would harvest public data about anyone that liked a page or a post that the candidate put on his campaign page in order to find the supporter's address. Door-to-door volunteers were then able to see on the app the address and name of the right-wing candidate's supporters. The app was built by Paul Hatte who was a member of Sarkozy's campaign team. According to Hatte's correspondance with CNIL, the authority considered that the app was legal, despite its guidelines prohibiting the combination of data from different sources.
For more information see Report by TacticalTech and Judith Duportail "The 2017 Presidential Election: The arrival of targeted political speech in French politics" and this article from Le Monde.