In Forbes, Parmy Olsen has uncovered what appears to be the first use of data from a personal fitness tracker in court, thanks to a personal injury suit currently under way in Canada. The plaintiff, a Calgary woman, plans to use data from her Fitbit to show how her activity levels have declined since the accident. Crucially, the data is being routed through a third-party analytics firm called Vivametrica, which will analyze the data and report its findings to the court, rather than submitting raw data directly into evidence.

Lawyers are using FitBit data in a civil suit. Obviously cops are gonna demand data for criminal prosecutions. http://t.co/Mcp0wW2o1a — J. Edgar Hitler (@onekade) November 17, 2014

Still, the case represents a new and unexpected use for personal data, and a potentially troubling precedent as the court's access to such data increases. It's easy to imagine the same data being used to establish or disprove a defendant's alibi in a criminal case. In this case, the subject volunteered her data to the court, but it could just as easily be obtained through by subpoena if the court deems it central to the case. The legal rules for such orders have yet to be set, but cases like this one make a huge difference in establishing those precedents. And while today's Fitbit customers don't think of their trackers as leaving a trail of evidence, that could quickly change as courts become more familiar with the devices.