After Strava, Polar is Revealing the Homes of Soldiers and Spies - bellingcat

"By showing all the sessions of an individual combined onto a single map, Polar is not only revealing the heart rates, routes, dates, time, duration, and pace of exercises carried out by individuals at military sites, but also revealing the same information from what are likely their homes as well. Tracing all of this information is very simple through the site: find a military base, select an exercise published there to identify the attached profile, and see where else this person has exercised. As people tend to turn their fitness trackers on/off when leaving or entering their homes, they unwittingly mark their houses on the map. Users often use their full names in their profiles, accompanied by a profile picture — even if they did not connect their Facebook profile to their Polar account."